| 单词 | radicle |
| 例句 | The root system is usually anchored by one main root developed from the embryonic radicle. Concepts of Biology 2013-04-25T00:00:00Z When the plant embryo emerges from the seed, the radicle of the embryo forms the root system. Biology for AP Courses 2022-06-09T00:00:00Z But instead of having just one root, most plants have millions of individual roots, each with a single radicle. Are plants intelligent? New book says yes 2015-08-04T04:00:00Z In these cases the cotyledons are plane; but they may be folded upon themselves and round the radicle, as in Mustard, where they are conduplicate, thus o>>. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z At the extremity most remote from the hilum, as the embryo, or inverted with respect to the seed, as the radicle. Webster's Unabridged Dictionary 2012-03-24T02:00:23.513Z The zygote develops into an embryo with a radicle, or small root, and one or two leaf-like organs called cotyledons. Concepts of Biology 2013-04-25T00:00:00Z Darwin found, moreover, by experiment, that, when the tip of a radicle is burnt or cut, "it transmits an influence to the upper adjoining part, causing it to bend away from the affected side." A Review of the Systems of Ethics Founded on the Theory of Evolution 2012-03-17T02:01:00.033Z Moreover, Darwin – who studied plants meticulously for most of his life, observed that the radicle – the root tip – “acts like the brain of one of the lower animals.” Are plants intelligent? New book says yes 2015-08-04T04:00:00Z Cotyledons incumbent, folded around the radicle.—Annuals or biennials, with yellow flowers. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z Venous emboli are those which approach the heart by the peripheral veins of the body or the pulmonary veins, and the liver by the radicles of the portal vein. A System of Practical Medicine by American Authors, Vol. I Volume 1: Pathology and General Diseases 2012-03-17T02:00:54.097Z A relation of another kind is the alteration in crystalline form resulting from the replacement in the chemical molecule of one or more atoms by atoms or radicles of a different kind. Encyclopaedia Britannica, 11th Edition, Volume 7, Slice 7 "Crocoite" to "Cuba" 2012-01-22T03:00:24.397Z It is true that the plant does not react with the rapidity which characterizes the animal; Darwin found that radicles are not sensitive to temporary contact, but only to long, though to slight pressure. A Review of the Systems of Ethics Founded on the Theory of Evolution 2012-03-17T02:01:00.033Z Mancuso has found rising evidence that the key to plant intelligence is in the radicle or root apex. Are plants intelligent? New book says yes 2015-08-04T04:00:00Z Cotyledons very thick and fleshy, their contiguous faces coherent, remaining under ground in germination; plumule 2-leaved; radicle curved.—Trees or shrubs. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z It is possible that they may further obtain access into the circulation through the radicles which furnish the communications between the capillaries and the lymphatics. A System of Practical Medicine by American Authors, Vol. I Volume 1: Pathology and General Diseases 2012-03-17T02:00:54.097Z The yellow gas was therefore supposed to be, and was called, "oxidized muriatic acid," and muriatic acid was itself regarded as composed of oxygen and an unknown substance or radicle. Heroes of Science Chemists 2011-12-09T03:00:21.047Z The radicles did not present the appearance of having been subjected to a sufficient pressure to account for their curvature. A Review of the Systems of Ethics Founded on the Theory of Evolution 2012-03-17T02:01:00.033Z In the early or mild forms, it consists of congestion in the veins or venous radicles, and effusions into the cellular tissue. The American Reformed Cattle Doctor 2011-11-14T03:00:19.813Z Seed erect; radicle inferior.—Perennial herbs, with pinnate or lyrate leaves. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z The growth of the primary root is limited; sooner or later adventitious roots develop from the axis above the radicle which they ultimately exceed in growth. Encyclopaedia Britannica, 11th Edition, Volume 12, Slice 3 "Gordon, Lord George" to "Grasses" 2011-11-13T03:00:13.177Z The reader will not fail to observe how essentially atomic is this conception of compound radicle. Heroes of Science Chemists 2011-12-09T03:00:21.047Z Sachs discovered that the radicle a little above the apex is sensitive and bends like a tendril towards the touching object. A Review of the Systems of Ethics Founded on the Theory of Evolution 2012-03-17T02:01:00.033Z Now, the premature development of these fibrous radicles, or roots, debilitates the tuber; in short, we have a sick potato. The American Reformed Cattle Doctor 2011-11-14T03:00:19.813Z Embryo straight, cotyledons very thick, radicle very short.—Low tender annuals, with alternate pinnate leaves and no stipules. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z Some plants will throw out radicles at any point indifferently along the internodes or merithallus. American Pomology Apples 2011-10-03T02:00:29.477Z The conception of compound radicle was carried by Berzelius to its utmost limits. Heroes of Science Chemists 2011-12-09T03:00:21.047Z As the apex of a radicle in penetrating the ground must be pressed on all sides, we wished to learn whether it could distinguish between harder, or more resisting, and softer substances. A Review of the Systems of Ethics Founded on the Theory of Evolution 2012-03-17T02:01:00.033Z According to the mode in which the seed is attached to the pericarp, the radicle may be directed upwards or downwards, or laterally, as regards the ovary. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 3 "Frost" to "Fyzabad" 2011-08-15T02:00:28.473Z Cotyledons large, thick or thickish; radicle incurved.—Leaves simple or simply compound, the earliest ones in germination usually opposite, the rest alternate; leaflets almost always quite entire. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z In fact all the so-called "compound radicles" which enter so largely into our study of organic chemistry are groups of two or atoms of two or more elements that behave as simple bodies. The Gospel Of Evolution From "The Atheistic Platform", Twelve Lectures 2011-05-31T02:00:36.420Z Benzoic acid they regarded as a compound of the same radicle with another radicle, consisting of equal numbers of oxygen and hydrogen atoms. Heroes of Science Chemists 2011-12-09T03:00:21.047Z Hydrogen is given off at the negative electrode, while at the positive electrode the uncharged SO4 radicle reacts with the water present, and oxygen is released. The New Gresham Encyclopedia Volume 4, Part 2: Ebert to Estremadura 2011-04-14T02:00:56.200Z The radicle r is folded on the edges of the cotyledons c which are accumbent. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 3 "Frost" to "Fyzabad" 2011-08-15T02:00:28.473Z Seeds in 2 rows in each cell, rounded, broadly winged; cotyledons accumbent; radicle short.—A low annual, with once or twice pinnatifid leaves and leafy-bracteate racemes of yellow flowers. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z These substances are the hydrates of the so-called alkaline metals, and may be compared to water in which part of the hydrogen is replaced by a metallic radicle. The New Gresham Encyclopedia. Vol. 1 Part 3 Atrebates to Bedlis To this compound radicle he gave the name of ammonium. Heroes of Science Chemists 2011-12-09T03:00:21.047Z These ions are chemical radicles carrying a definite electric charge. The New Gresham Encyclopedia Volume 4, Part 2: Ebert to Estremadura 2011-04-14T02:00:56.200Z The radicle and cotyledons are either straight or variously curved. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 3 "Frost" to "Fyzabad" 2011-08-15T02:00:28.473Z Embryo straightish, with a short radicle, and thin longitudinally plaited cotyledons.—Shrubs or small trees, with large and showy white flowers on axillary peduncles. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z The alkalies may be regarded as water in which part of the hydrogen is replaced by a metallic radicle. The New Gresham Encyclopedia. Vol. 1 Part 1 A to Amide The group of atoms thus removable—the compound radicle—may exist in a series of compounds. Heroes of Science Chemists 2011-12-09T03:00:21.047Z The kind of charge, positive or negative, depends on the nature of the radicle. The New Gresham Encyclopedia Volume 4, Part 2: Ebert to Estremadura 2011-04-14T02:00:56.200Z In other divisions the radicle is folded in a spiral manner, and the cotyledons follow the same course. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 3 "Frost" to "Fyzabad" 2011-08-15T02:00:28.473Z Carpels as in Malva, or else as in Sida, but the solitary kidney-shaped seed ascending and the radicle pointing downward, as in the former. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z The amides are formed by replacing one of the hydrogen atoms of ammonia by an acid radicle, e.g. The New Gresham Encyclopedia. Vol. 1 Part 1 A to Amide The compounds of ammonium possess many properties in common, and this is partly explained if we assume that they all contain one or more atoms of the compound radicle ammonium. Heroes of Science Chemists 2011-12-09T03:00:21.047Z The ions exhibit none of the chemical properties of the uncharged radicle. The New Gresham Encyclopedia Volume 4, Part 2: Ebert to Estremadura 2011-04-14T02:00:56.200Z The radicle is developed from the lower part of the axis r. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 3 "Frost" to "Fyzabad" 2011-08-15T02:00:28.473Z Inverted and straight, with the micropyle next the hilum and the radicle consequently inferior. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z The amines are compounds formed by the introduction of alcohol radicles into ammonia, e.g. The New Gresham Encyclopedia. Vol. 1 Part 1 A to Amide The conceptions of compound radicles and of substitution held some such position in organic chemistry as that which I have now attempted to indicate when Dumas and Liebig began their work in this field. Heroes of Science Chemists 2011-12-09T03:00:21.047Z An uncharged SO4 radicle would react with the water present, and sulphuric acid would be formed and oxygen liberated. The New Gresham Encyclopedia Volume 4, Part 2: Ebert to Estremadura 2011-04-14T02:00:56.200Z The radicle r is folded on the back of the cotyledons c, which are said to be incumbent. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 3 "Frost" to "Fyzabad" 2011-08-15T02:00:28.473Z Seeds anatropous, mostly single in each cell, large and flat, with a smooth coriaceous integument; the embryo shorter than the hard albumen, with a long radicle and flat cotyledons. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z Incumbent, leaning or resting upon; the cotyledons are incumbent when the back of one of them lies against the radicle, 128; the anthers are incumbent when turned or looking inwards. The Elements of Botany For Beginners and For Schools The oxygen atom in this nucleus is very strongly basic and exhibits its quadrivalent property by forming stable salts by direct addition of acid radicles. The Chemistry of Plant Life Cotyledons opened to show the radicle a, and the plumule. Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 4 "Carnegie Andrew" to "Casus Belli" In an orthotropal seed the embryo is inverted or antitropal, the radicle pointing to the apex of the seed, or to the part opposite the hilum. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 3 "Frost" to "Fyzabad" 2011-08-15T02:00:28.473Z Embryo nearly the length of the albumen; radicle slender, as long as or longer than the flat cotyledons. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z In one very natural family, the Crucifer�, two different modes prevail in the way the two cotyledons are brought round against the radicle. The Elements of Botany For Beginners and For Schools Thus, taking the specific ionic velocity of hydrogen as 0.00032 cm. per second, we can find, by determining the conductivity of dilute solutions of any acid, the specific velocity of the acid radicle involved. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 8 "Conduction, Electric" Like many young mathematicians he attacked the problem of resolving the higher algebraic equations, notwithstanding Abel’s proof that a solution by radicles was impossible. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 6 "Cockaigne" to "Columbus, Christopher" Again, the cotyledons are conduplicate when the radicle is dorsal, and enclosed between their folds. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 3 "Frost" to "Fyzabad" 2011-08-15T02:00:28.473Z Embryo thick, the cotyledons incumbent upon the radicle.—Low saline plants, with succulent leafless jointed stems, and opposite branches; the flower-bearing branchlets forming the spikes. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z Incumbent, or with the plane of the cotyledons brought up in the opposite direction, so that the back of one of them lies against the radicle, as shown in Fig. The Elements of Botany For Beginners and For Schools Or again, since we know the specific velocity of silver, we can find the velocities of a series of acid radicles at great dilution by measuring the conductivity of their silver salts. Encyclopaedia Britannica, 11th Edition, Volume 6, Slice 8 "Conduction, Electric" The radicles, or commencement of the veins, in many, and it may be in all parts of the body, perform the office of absorption. A Treatise on Anatomy, Physiology, and Hygiene (Revised Edition) It has been already stated that the radicle of the embryo is directed to the micropyle, and the cotyledons to the chalaza. Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 3 "Frost" to "Fyzabad" 2011-08-15T02:00:28.473Z Embryo placed in a groove on the outside of the albumen and curved half-way around it; the radicle and usually the cotyledons slender.—Pedicels jointed. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z In lieu of a face I saw a raw and shining polyp, a mass of waving, tossing, pulpy radicles from whose centre shone two long, obliquely set, pale eyes, ablaze with devilry and malice. Byways of Ghost-Land The envelope breaks, the little plant makes its appearance; radicle and stalk come to light. The Industries of Animals Thus, wherever there is a minute artery to deposit a living particle of matter, there is a lymphatic vessel, or venous radicle, to remove it as soon as it shall have finished its particular office. A Treatise on Anatomy, Physiology, and Hygiene (Revised Edition) Watery drinks are absorbed in the stomach and intestines, by the radicles of the vena portæ. North American Medical and Surgical Journal, Vol. 2, No. 3, July, 1826 Cotyledons fleshy and oily, sinuous or corrugated, 2-lobed; radicle short, superior. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z The radicle is blunt and is about 3⁄4 mm in length, while the cotyledons are 1⁄2 mm long. All About Coffee It is the young plant which absorbs the glucose, and which must therefore be destroyed; they cut off the radicle with their mandibles, and gnaw the stalk; the germ is thus suppressed. The Industries of Animals Give the etymologies of the words icicle, radicle, and radical. A Handbook of the English Language Planting nuts with the radicle end down invariably produced seedlings with undesirable crooks in the root-stem region which made them unsuitable for grafting. Northern Nut Growers Association Report of the Proceedings at the Thirty-Seventh Annual Report Wooster, Ohio, September 3, 4, 5, 1946 Embryo small, at the apex of copious albumen; radicle directed upward; cotyledons cylindrical. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z The axis, which is differentiated into the plumule directed upward and the radicle downward, is small and straight and it is covered more or less by the edges of the scutellum. A Handbook of Some South Indian Grasses I think it probable that the words greed, greedily, are from the same radicle. Notes and Queries, Number 52, October 26, 1850 A Medium of Inter-communication for Literary Men, Artists, Antiquaries, Genealogists, etc The amount of the boric acid radicle may be determined by incinerating 5-10 grammes of soap, extracting with hot dilute acid, filtering, neutralising this solution to methyl orange, and boiling to expel carbon dioxide. The Handbook of Soap Manufacture Planting nuts radicle end up produced straighter seedlings than planting them on their side. Northern Nut Growers Association Report of the Proceedings at the Thirty-Seventh Annual Report Wooster, Ohio, September 3, 4, 5, 1946 Cotyledons remaining underground in germination; radicle very short, included.—Flowers greenish or yellowish. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z Four of these amylin radicles are grouped centrally round the fifth, thus:— Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3 "Brescia" to "Bulgaria" The "germ" is the radicle of the cacao seed, or that part of the cacao seed which on germination forms the root. Cocoa and Chocolate Their History from Plantation to Consumer Recent work, however, has shown the existence of several so-called mixed glycerides, in which the hydroxyls of the same molecule of glycerol are displaced by two or sometimes three different acid radicles. The Handbook of Soap Manufacture I have bought me a lot, about a hectare, And have built me a house ten metres square, And soon, I think, I shall take her there, My tart little acid radicle. Modern Eloquence: Vol III, After-Dinner Speeches P-Z Embryo terete, in the axis of copious albumen, with a slender inferior radicle and very small cotyledons. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z The pebbles, though they contain the same chemical elements, do not become active and put out a radicle. The Breath of Life It grows about four or five inches high, with branched stems bearing very succulent, kidney-shaped leaves opposite each other—the radicle leaves on long foot-stalks, whilst those of the stem-leaves are much shorter. Chambers's Edinburgh Journal, No. 427 Volume 17, New Series, March 6, 1852 The alkaline, or soapy taste, is the perception of hydroxyl radicles charged with negative electricity. Creative Chemistry Descriptive of Recent Achievements in the Chemical Industries The round pointed projection was formerly called the radicle, but is now spoken of as the hypocotyl, because it grows below or under the cotyledons. The First Book of Farming Cotyledons elliptical; radicle slender.—Light timber-trees, with petioled pinnate leaves of 3–15 either toothed or entire leaflets; the small flowers in crowded panicles or racemes from the axils of last year's leaves. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z There is this certain about them, that they depend on the presence of vascular tissue, from which the radicles or the divisions of each root originate: see young Hyacinth roots, grown in water. Journals of Travels in Assam, Burma, Bhootan, Afghanistan and the Neighbouring Countries "No, but suppose you were to plant it upside down, with the plantule above and the radicle below; do you think it would grow that way?" Willis the Pilot The capsici, somewhat similar in flavour to the pea, are detached from the radicles of a plant with a flower strikingly like the potatoe, and is used for a similar purpose to the jugulena. Blackwood's Edinburgh Magazine — Volume 56, No. 345, July, 1844 We grub up, on the gardener's hint and permission, some of the Cameris humilis, to whose filamentous radicles are attached certain little grains, of great sweetness and flavour. Blackwood's Edinburgh Magazine — Volume 53, No. 332, June, 1843 Seed erect; radicle inferior.—Low perennial herbs, with chiefly radical 3–5-lobed or divided leaves, and small yellow flowers on bracted scapes. The Manual of the Botany of the Northern United States Including the District East of the Mississippi and North of North Carolina and Tennessee 2012-04-12T02:00:30.140Z The caudex is altogether similar in structure to that of Alsophyla, equally furnished with strong black bristly radicles towards its base. Journals of Travels in Assam, Burma, Bhootan, Afghanistan and the Neighbouring Countries "At first the radicle or root would begin by growing upwards, and the plantule or germ would descend." Willis the Pilot And, lastly, that at the apex of the nucleus the radicle of the future Embryo would constantly be found. Narrative of a Survey of the Intertropical and Western Coasts of Australia Performed between the years 1818 and 1822 — Volume 2 The soil, it appears, is suited to the seed, for it has sent its radicle downward, and it may now send its shoot upward also with confidence. Walden In the plant, the eye or germinative point opens to a leaf, then to another leaf, with a power of transforming the leaf into radicle, stamen, pistil, petal, bract, sepal, or seed. Representative Men Are the sheaths found on certain radicles strictly confined to monocotyledonous plants. Journals of Travels in Assam, Burma, Bhootan, Afghanistan and the Neighbouring Countries "Plantule and radicle are ambitious words, my dear brother; recollect that you are speaking to simple mortals." Willis the Pilot Of the two Rumex seeds, one died and the other germinated; but its radicle was brown and soon withered. Insectivorous Plants This movement of the radicle has been described in Brassica, Aesculus, Phaseolus, Vicia, Cucurbita, Quercus and Zea. The Power of Movement in Plants Drifting into shallow water the sharp end of the spindly radicle bores into the mud. Confessions of a Beachcomber We may imagine a case in which the primary radicle may be without a sheath, while its divisions shall have them, this depending on the want of adhesion of the cuticle over the original one. Journals of Travels in Assam, Burma, Bhootan, Afghanistan and the Neighbouring Countries The three atoms of hydrogen may in like manner be replaced by alcohol radicles, forming acid and neutral ethers. The Story of the Soil; from the Basis of Absolute Science and Real Life, Two mustard seeds germinated; but their cotyledons were marked with brown patches and their radicles deformed. Insectivorous Plants Aesculus hippocastanum: outlines of tracks left on inclined glass-plates by tips of radicles. The Power of Movement in Plants One floating radicle with its pent-up energy, having after weeks of drifting and swaying this way and that to the slightest current and ripple, grapples Mother Earth and makes a law to the ocean. Confessions of a Beachcomber What is the cause of the plurality of radicles in certain species of Lemna, and their blank in others? Journals of Travels in Assam, Burma, Bhootan, Afghanistan and the Neighbouring Countries But what is that force which divides and subdivides the branches of a tree into smaller boughs and its roots into radicles? Laughter : an Essay on the Meaning of the Comic Both seeds of the Avena germinated, one grew well, the other had its radicle brown and withered. Insectivorous Plants Phaseolus multiflorus: tracks left on inclined smoked glass-plates by tips of radicles in growing downwards. The Power of Movement in Plants Whole battalions of living mangrove radicles fall into the rivers during February and March. Confessions of a Beachcomber This enclosure arises entirely from the excessive tendency to cohesion between the roots and radicles of some of the species of this genus. Journals of Travels in Assam, Burma, Bhootan, Afghanistan and the Neighbouring Countries Is there any radicle of such legislation in our parliamentary system? Bernard Shaw's Preface to Major Barbara This seedling had an extremely short, crooked, diseased, radicle, with no absorbent hairs; and the cotyledons were oddly mottled with purple, with the edges blackened and partly withered. Insectivorous Plants Hypocotyl.—A seed lying on damp sand was firmly fixed by two crossed wires and by its own growing radicle. The Power of Movement in Plants Its radicles resemble pipe-stems, or as they lie stranded on the beach, slightly curved and with the brown tapering calyx tube attached, green snakes with pointed beads. Confessions of a Beachcomber The radicle of the germinating seed is not more persevering, not more determined to descend into the cool damp earth. Fabre, Poet of Science It is the tip of the radicle of a germinating common bean. More Letters of Charles Darwin — Volume 2 It gives me great pleasure to fancy that I see radicles of orchid seed penetrating the Sphagnum. More Letters of Charles Darwin — Volume 1 Nine radicles were next arranged in the manner formerly described, so that in growing downwards they left tracks on smoked glass-plates, inclined at various angles between 45o and 80o beneath the horizon. The Power of Movement in Plants Thus the main divisions of flowering plants are founded on differences in the embryo—on the number and position of the cotyledons, and on the mode of development of the plumule and radicle. The Origin of Species by means of Natural Selection, 6th Edition Ten radicles were extended horizontally on and beneath a layer of damp friable peat-earth; and before being extended their tips were touched with dry caustic on the upper side. The Power of Movement in Plants The tip of the radicle is a kind of brain to the whole growing part of the radicle! More Letters of Charles Darwin — Volume 2 Ten other radicles similarly placed were touched on the lower side; and this would tend to make them bend from the cauterised side; and therefore, as now placed, upwards, or in opposition to geotropism. The Power of Movement in Plants Consequently, as long as the radicle continued to increase in length and remained straight, the weighted bean would be lifted up after the tip had reached the bottom of the shallow hole. The Power of Movement in Plants Phaseolus multiflorus.—Eight radicles, serving as controls, were extended horizontally, some in damp friable peat and some in damp air. The Power of Movement in Plants The course pursued by the radicle in penetrating the ground must be determined by the tip; hence it has acquired such diverse kinds of sensitiveness. The Power of Movement in Plants Now it seems possible that a circle between radicle and hypocotyl may be permeable to fluids, and thus have given rise to projections so as to expose larger surface. More Letters of Charles Darwin — Volume 2 Radicles of Sinapis alba.—The radicles of some plants are indifferent, as far as curvature is concerned, to the action of light; whilst others bend towards and others from it.* The Power of Movement in Plants We succeeded better in ascertaining the force exerted transversely by these radicles. The Power of Movement in Plants The radicles of Sinapis alba, when immersed in water and exposed to a lateral light, bend from it, or are apheliotropic. The Power of Movement in Plants At the same time the tips of 54 other radicles, similarly exposed, were just touched with nitrate of silver. The Power of Movement in Plants Could you test Welwitschia with permanganate of potassium: if, like my pegs, the lower surface would be coloured brown like radicle, and upper surface left white like hypocotyl. More Letters of Charles Darwin — Volume 2 We had previously tried hundreds of unmutilated radicles under similar circumstances, and found that every one that was healthy became plainly geotropic in under 12 h. The Power of Movement in Plants The stick was then suspended horizontally by a fine wire passing through the hole lately filled by the radicle, and a little saucer was suspended beneath to receive the weights; and it required 8 lbs. The Power of Movement in Plants Hence it seems probable that Sachs unintentionally amputated the radicles on which he experimented, not strictly in a transverse direction. The Power of Movement in Plants The terminal growing part, 10 mm. in length, of the cauterised radicles had increased in this interval to a mean length of 24.5 mm., and of the controls to a mean of 26 mm. The Power of Movement in Plants But as the cauterised radicles had more than doubled their length in the 24 h., it is manifest that they had not been seriously injured by the caustic. The Power of Movement in Plants Many trials were made, by coating the tips of horizontally extended radicles with the before described thick grease. The Power of Movement in Plants Cyclamen Persicum: seedling, figure enlarged: c, blade of cotyledon, not yet expanded, with arched petiole beginning to straighten itself; h, hypocotyl developed into a corm; r, secondary radicles. The Power of Movement in Plants Nine young radicles between .3 and .5 inch in length, with their tips cauterised and blackened for a length never exceeding ½ mm., together with eight control specimens, were extended horizontally in damp air. The Power of Movement in Plants These radicles were examined after 9 h. and again after 24 h. The Power of Movement in Plants Concluding Remarks.—Abundant evidence has now been given, showing that with various plants the tip of the radicle is alone sensitive to geotropism; and that when thus excited, it causes the adjoining parts to bend. The Power of Movement in Plants The curvature of one of these four radicles almost disappeared after 24 h. The Power of Movement in Plants We shall hereafter see that many seedlings are protected from frost, but by a widely different process, namely, by being drawn beneath the surface by the contraction of their radicles. The Power of Movement in Plants These two, latter radicles continued during two more days to grow in the peat in the same directions, that is, at an angle of 45o beneath the horizon and horizontally. The Power of Movement in Plants Vicia faba: radicle, rectangularly bent at A, after the amputation of the tip, due to the previous influence of geotropism. The Power of Movement in Plants A, point of chief curvature of the radicle, whilst standing vertically downwards. The Power of Movement in Plants In the previously given experiments on 29 horizontally extended radicles with their tips amputated, only one grew irregularly in any marked manner, and this became bowed upwards at an angle of 65o. The Power of Movement in Plants The radicle begins in a few weeks to enlarge into a little tuber, which then abounds with starch and is only slightly bitter. The Power of Movement in Plants In Ciesielski's experiments the radicles could not have grown very irregularly, for if they had done so, he could not have spoken confidently of the obliteration of all geotropic action. The Power of Movement in Plants We also tried touching both the upper and the lower sides of the tips of some radicles of the bean, extended horizontally in damp friable earth. The Power of Movement in Plants A dot had been made on all six radicles at 10 mm. from their tips, when first placed horizontally. The Power of Movement in Plants I. that the secondary radicles of Cucurbita made serpentine tracks on a smoked glass-plate, they clearly circumnutated, and there can hardly be a doubt that this holds good with other secondary radicles. The Power of Movement in Plants After they have protruded from the seed, they are united at their lower ends with the undeveloped hypocotyl and undeveloped radicle, which together form a point only about .1 inch in length. The Power of Movement in Plants The same number of uncauterised radicles of the same age were observed as controls. The Power of Movement in Plants Nineteen young radicles with cauterised tips were extended at different times horizontally over water. The Power of Movement in Plants In the first trial, the tips of three radicles were lightly touched with the caustic for 6 or 7 seconds, which was a longer application than usual. The Power of Movement in Plants As we had observed that grease was highly injurious to some plants, we determined to try its effects on radicles. The Power of Movement in Plants Firstly a filament was fixed to the basal leg of an arched hypocotyl close above the summit of the radicle. The Power of Movement in Plants The tips of 33 other radicles were coated on different occasions for a length of 3 mm.; and they were compared with the controls after 8 h., The Power of Movement in Plants Pisum sativum.—Five radicles, extended horizontally over water, had their tips lightly touched two or three times with dry caustic. The Power of Movement in Plants Six control radicles all became slightly geotropic in 4 h., and strongly so after 8 h. The Power of Movement in Plants The first change is the protrusion of the radicle, which begins at once to circumnutate. The Power of Movement in Plants Quercus robur: tracks left on inclined smoked glass-plates by tips of radicles in growing downwards. The Power of Movement in Plants After 24 h. several of the amputated radicles remained horizontal, but some showed a trace of geotropism, and one was plainly geotropic, for it was inclined at 40o beneath the horizon. The Power of Movement in Plants It is of more importance that Sachs found that the rate of growth of the different parts of radicles with amputated tips was the same as with unmutilated ones. The Power of Movement in Plants The cauterised radicles increased greatly in length, but the measurements are not worth giving. The Power of Movement in Plants It thus could not have checked much, if at all, the growth of the terminal part of the radicle. The Power of Movement in Plants Four radicles were allowed to grow downwards over plates of smoked glass, inclined at 70o to the horizon, under the Fig. The Power of Movement in Plants The following case proves that the action of the caustic by itself does not prevent the curvature of the radicle. The Power of Movement in Plants Of the four horizontal radicles, one alone showed a trace of geotropism; of the three up-curved radicles, one retained this curvature, and the other two had become horizontal. The Power of Movement in Plants The radicles with their tips cut off had grown in the 24 h. The Power of Movement in Plants But after three or four days when new vegetative points were formed, the radicles were again acted on by geotropism, and now they curved themselves perpendicularly downwards. The Power of Movement in Plants These radicles were so delicate that they rarely had the power to sweep the glasses quite clean. The Power of Movement in Plants In the case of the radicles of Sinapis alba, sensitiveness to light also resides in the tip, which, when laterally illuminated, causes the adjoining part of the root to bend apheliotropically. The Power of Movement in Plants We may therefore safely conclude that the mere application of caustic to the tip does not prevent the radicles from bending. The Power of Movement in Plants Vicia faba: state of radicles which had been extended horizontally for 23 h. The Power of Movement in Plants It would be superfluous to describe in detail the behaviour of the 10 remaining cauterised radicles. The Power of Movement in Plants Epicotyl.—At the point where the radicle had protruded from a bean laid on its side, a flattened solid lump projected .1 of an inch, in the same horizontal plane with the bean. The Power of Movement in Plants After 24 h., and again after 32 h. from the commencement, four of the cauterised radicles were still horizontal, but one was plainly geotropic, being inclined at 45o beneath the horizon. The Power of Movement in Plants The length of the radicles was not measured in either set, but it was manifest that the cauterised radicles had grown greatly. The Power of Movement in Plants Gossypium herbaceum.—The radicles of this plant bend, through the action of geotropism, for a length of about 6 mm. The Power of Movement in Plants Of 5 cauterised radicles of Gossypium herbaceum, 4 remained horizontal for 23 h. and 1 became slightly geotropic; 6 control radicles were distinctly geotropic in 7 h. The Power of Movement in Plants In B the plate was inclined 65o with the horizon, and the radicle was a trifle larger. The Power of Movement in Plants The tips of nine radicles were coated for a length of 3 mm., and after 7 h. The Power of Movement in Plants We may therefore conclude that grease on the tips of the radicles of this Phaseolus somewhat delays and lessens the geotropic curvature of the part which ought to bend most. The Power of Movement in Plants Five radicles, placed horizontally in damp air, had their tips touched with caustic, and the discoloration extended for a length of from 2/3 to 1 mm. The Power of Movement in Plants Thirdly, the point of the radicle is so fine that it is difficult not to cauterise it either too much or too little. The Power of Movement in Plants These radicles therefore were continually moving in all directions—that is, they circumnutated. The Power of Movement in Plants Ten radicles were laid horizontally beneath and on damp friable peat, and their tips were touched with caustic on the upper side. The Power of Movement in Plants The radicles of this plant, as already remarked, do not succeed well in damp air, but the result of one trial may be briefly given. The Power of Movement in Plants The eight cauterised radicles which had at first a mean length of .36 inch, after 9 h. had increased to a mean length of .79 inch; and after 24 h. The Power of Movement in Plants A few of the control radicles were measured after 25 h., and they were on an average only a little longer than the cauterised, viz., The Power of Movement in Plants Vicia faba: tracks left on inclined smoked glass-plates, by tips of radicles in growing downwards. The Power of Movement in Plants It is again the tip which is alone sensitive, at least in some cases, to moisture, causing the radicle to bend towards its source. The Power of Movement in Plants From unknown causes, nutriment is sometimes stored in the hypocotyl or in the radicle, and then one of the cotyledons or both become rudimentary, of which several instances have been given. The Power of Movement in Plants Nine other radicles were similarly extended, three in damp peat and six in damp air, and dry caustic was held transversely to their tips during 4 or 5 seconds. The Power of Movement in Plants In the same box there were 15 control radicles, mostly about .36 inch in length, but some rather longer and older, and therefore less sensitive. The Power of Movement in Plants We presume therefore that the friction of the apex on the smoked surface, little as this could have been, sufficed to check the movement from side to side of these delicate radicles. The Power of Movement in Plants There was no plain difference in length between the five well cauterised radicles which remained horizontal, and the three with slightly cauterised tips which had become abruptly bent down. The Power of Movement in Plants Lastly 12 radicles were subjected to a temperature varying between 72o and 85o F., and none of them were in the least affected by the squares. The Power of Movement in Plants Bearing this fact in mind, it should be observed that the length of the curved part of the radicle, which had become deflected from the cauterised side in the course of 8 h. The Power of Movement in Plants Geotropism, as was shown in the last chapter, excites the primary radicle to bend downwards with very little force, quite insufficient to penetrate the ground. The Power of Movement in Plants Zea mays: track left on inclined smoked glass-plate by tip of radicle in growing downwards. The Power of Movement in Plants The radicle first protrudes from a small hole at one end of the tough, leathery, winged fruit. The Power of Movement in Plants The tip of the radicle more curved than the upper part, but in the same plane. The Power of Movement in Plants After 23 h. the extreme tip was slightly bent towards the card; the general curvature of the radicle remaining the same. The Power of Movement in Plants A radicle of considerable length had a small square of card fixed with shellac to its apex laterally: after only 7 h. The Power of Movement in Plants In the case previously described the basal part of the very short radicle from being turned vertically upwards, was at first very little affected by geotropism. The Power of Movement in Plants Square of card gummed to apex: after 9 h. slightly curved from card; next morning radicle straight, and apex had grown beyond the card. The Power of Movement in Plants Little square of tin-foil fixed with gum to one side of apex of a young and short radicle: after 15 h. no effect, but tin-foil had become displaced. The Power of Movement in Plants The seventh radicle which was not affected was apparently sickly, as it became brown on the following day; so that it formed no real exception. The Power of Movement in Plants The radicles looked healthy but grew very slowly. The Power of Movement in Plants THE following chapter is devoted to the circumnutating movements of the radicles, hypocotyls, and cotyledons of seedling plants; and, when the cotyledons do not rise above the ground, to the movements of the epicotyl. The Power of Movement in Plants The force of our evidence would have been greatly weakened if occasionally, though rarely, the radicles had become curved in any direction independently of the attached objects. The Power of Movement in Plants In our next trial the dried tips of 11 radicles were touched momentarily with dry caustic, and after a few minutes were immersed in water. The Power of Movement in Plants But there was moderately distinct deflection from the perpendicular and from the attached object in only one radicle out of this large number of cases. The Power of Movement in Plants Secondly, 5 oldish radicles, 1 ½ inch in length, and therefore less sensitive than the above-mentioned young ones, were similarly placed and similarly treated. The Power of Movement in Plants Another seed was treated and observed in the same manner, but the radicle in this case protruded .1 inch, and was not Fig. The Power of Movement in Plants Owing to the extreme tenuity of these radicles, it was very difficult to attach the square to the actual apex. The Power of Movement in Plants It is possible that some secondary radicles are more sensitive than others; for Sachs has proved* the interesting fact that each individual secondary radicle possesses its own peculiar constitution. The Power of Movement in Plants Haberlandt remarks,*** that these radicles in breaking through the seed-coats often rub and press against the ruptured edges, and consequently bend round them. The Power of Movement in Plants Twenty-eight radicles suspended vertically over water were thus treated on different occasions, and 13 of them became curved towards the cards. The Power of Movement in Plants Vicia faba: circumnutation of a radicle, at first pointing vertically upwards, kept in darkness, traced on a horizontal glass, during 14 hours. The Power of Movement in Plants There can therefore be no doubt that with the pea, irritation from a bit of card attached to one side of the radicle above the apex suffices to induce curvature. The Power of Movement in Plants These four radicles therefore did not seem Fig. The Power of Movement in Plants Thus 6 radicles, horizontally extended with attached squares, were tried on June 8th at a proper temperature, and after 7 h. The Power of Movement in Plants In such cases the opposite side continues to grow, and the radicle necessarily becomes bent towards the injured side. The Power of Movement in Plants The distance between the extreme right and left positions of the radicle A was 0.7 mm., ascertained in the same manner as in the case of Phaseolus. The Power of Movement in Plants The radicles did not keep healthy for long. The Power of Movement in Plants After 24 h. all 10 radicles had increased immensely in length; in 5 of them the curvature was nearly the same, in 2 it had increased, and in 3 it had decreased. The Power of Movement in Plants Thus 11 radicles out of the 15 were acted on. The Power of Movement in Plants On July 10th another trial was made with 6 horizontally extended radicles, with squares attached in the same manner beneath their tips; and after 7 h. The Power of Movement in Plants Even the stems of seedlings before they have broken through the ground, as well as their buried radicles, circumnutate, as far as the pressure of the surrounding earth permits. The Power of Movement in Plants Considering the unfavourable circumstances, and bearing in mind the case of the bean, the evidence appears sufficient to show that the tips of the secondary radicles of the pea are sensitive to slight contact. The Power of Movement in Plants The tips of 13 radicles, dried with blotting-paper, were thrice touched or just rubbed on one side with dry nitrate of silver. The Power of Movement in Plants Sensitiveness of the tips of the Secondary Radicles of the Bean to contact.—All the previous observations relate to the main or primary radicle. The Power of Movement in Plants Triticum vulgare.—Analogous trials were made on 8 radicles of the common wheat; and greasing their tips produced much less effect than in the case of the oats. The Power of Movement in Plants The distance between the extreme right and left positions of the radicle A, in its lateral movement, was 2 mm., as ascertained by measurement with an eye-piece micrometer. The Power of Movement in Plants We also modified the experiment, by pinching young radicles a little way above their tips, between the arms of a U-shaped piece of thick leaden wire. The Power of Movement in Plants Five radicles had their ends cut off, and served as controls or standards. The Power of Movement in Plants By this latter time a sixth radicle had become bent at a right angle from the side bearing the square. The Power of Movement in Plants Sachs made the interesting discovery, a few years ago, that the radicles of many seedling plants bend towards an adjoining damp surface.* The Power of Movement in Plants On the other hand, if the tip is subjected to the vapour of water proceeding from one side, the upper part of the radicle bends towards this side. The Power of Movement in Plants The tips of 5 radicles were cauterised with nitrate of silver, and about 1 mm. in length was thus destroyed. The Power of Movement in Plants It appears from these cases that a cap of goldbeaters' skin checks, though only to a slight degree, the bending of the radicles to an adjoining damp surface. The Power of Movement in Plants Some of these secondary radicles adhered together or had become confluent. The Power of Movement in Plants The radicles of the pea were tried with attached objects and caustic, both of which acted. The Power of Movement in Plants Brassica oleracea: circumnutation of radicle, traced on horizontal glass, from 9 A.M. The Power of Movement in Plants Quercus robur: Sensitiveness of the apex of the Radicle.—The tips of the radicles of the common oak are fully as sensitive to slight contact as are those of any plant examined by us. The Power of Movement in Plants This fact having been ascertained, little squares of the card-like paper were affixed with shellac, on several occasions, to the tips of 68 radicles. The Power of Movement in Plants For instance, the terminal growing part of one radicle was bent upwards into a rectangle in 8 h. The Power of Movement in Plants The radicles of Tropaeolum were highly sensitive to contact; and so, as far as we could judge, were those of Gossypium herbaceum, and they were certainly sensitive to caustic. The Power of Movement in Plants Of the 54 cauterised radicles one case was doubtful, 25 curved themselves from the light in the normal manner, and 28, or more than half, were not in the least apheliotropic. The Power of Movement in Plants The tips of the radicles of Cucurbita ovifera were likewise highly sensitive to caustic, though only moderately so to contact. The Power of Movement in Plants Nine radicles, similarly placed, had their tips touched on the lower side with the caustic; and after 24 h., The Power of Movement in Plants It is therefore clear that the tips of the radicles of this Phaseolus are much less sensitive to contact than are those of the bean or pea. The Power of Movement in Plants It is therefore certain that the apex of the radicle of this Phaseolus is extremely sensitive to caustic, more so than that of the bean, though the latter is far more sensitive to pressure. The Power of Movement in Plants Some of the radicles which were experimented on were young and short, most of them of moderate length, and two or three exceeded three inches in length. The Power of Movement in Plants Of the six radicles in damp air, three had their tips curved after an interval of 10 h. The Power of Movement in Plants Thus altogether six out of the ten secondary radicles were acted on, four not being affected. The Power of Movement in Plants Of 7 not cauterised radicles observed at the same time, all had come into contact with the sieve. The Power of Movement in Plants The tips of 11 radicles were protected by moistened gold-beaters' skin, which adheres closely, for a length varying from 1 ½ to 2 ½ mm. The Power of Movement in Plants Two other radicles of the cabbage travelled downwards in almost rectilinear courses. The Power of Movement in Plants In both these trials the radicles grew well; 7 of them, which were at first from 4 to 11 mm. in length, were after 11 h. between 7 and 16 mm.; The Power of Movement in Plants The radicles were examined on each successive morning, at nearly the same hour, that is, after intervals of 24 h. The Power of Movement in Plants This radicle suffered from a series of accidents, and acted in an anomalous manner, for the apex appeared at first insensible and afterwards sensitive to contact. The Power of Movement in Plants Moreover, 7 other radicles out of the 68, were slightly and two doubtfully deflected from the cards. The Power of Movement in Plants With Phaseolus multiflorus, 15 radicles were cauterised, and 8 remained horizontal for 24 h.; whereas all the controls were plainly geotropic in 8 h. The Power of Movement in Plants The control or ungreased radicles were not invariably attracted towards the bottom of the sieve. The Power of Movement in Plants Only 7 out of the 22 radicles became moderately deflected in from 3 to 5 days from the sliced surface, and several of the others grew irregularly. The Power of Movement in Plants Quercus robur: radicle with square of card attached to one side of apex, causing it to become hooked. The Power of Movement in Plants With the pea, therefore, the irritation from an attached object, and from geotropism when acting at right angles to the radicle, are nearly balanced forces. The Power of Movement in Plants Lastly, the tips of several radicles of Vicia faba and Phaseolus multiflorus were thickly coated with grease for a length of 3 mm. The Power of Movement in Plants Tip of radicle protected as in last case: after 11 h. no effect, but after 24 h. The Power of Movement in Plants Case like the last in all respects, except that a length of only .25 of an inch of the radicle was thus deflected. The Power of Movement in Plants Square of card affixed with shellac: after 24 h. no effect, but the radicle had not grown well and seemed sickly. The Power of Movement in Plants Next morning a square of card was fixed with shellac to it, and after 9 h. radicle greatly deflected from the card. The Power of Movement in Plants The radicle, therefore, supposing the seed to be lying on the surface, quickly bends downwards, following a more or less spiral course, as was seen on the smoked glass-plates. The Power of Movement in Plants Small square of sanded card, attached with thick gum-water laterally to the apex of a long straight radicle: after 9 h. greatly deflected from the perpendicular and from the card. The Power of Movement in Plants A narrow chip of a quill was fixed with shellac to the apex of a radicle. The Power of Movement in Plants Six of these were plainly acted on, and in two cases the radicles became coiled up into complete loops. The Power of Movement in Plants In our first trial on 15 radicles no effect was produced. The Power of Movement in Plants This force, combined with that due to transverse growth, gives to the radicle the power of a wedge. The Power of Movement in Plants These cases deserve notice, because when one side of the apex was just touched with caustic, the radicle, as we have seen, curved itself in an opposite direction, that is, away from the touched side. The Power of Movement in Plants The squares attached above the apex cause the radicle to bend abruptly, the part above and beneath remaining nearly straight; so that here there is little or no transmitted effect. The Power of Movement in Plants But out of this considerable number of trials only 5 radicles were plainly bent, and 8 others slightly or even doubtfully, from the attached objects; the remaining 46 not being at all affected. The Power of Movement in Plants The effect of cutting off with a razor a thin slice from one side of the conical apex of 14 young and short radicles was next tried. The Power of Movement in Plants Whether this can be of any service to them is very doubtful, but with seeds germinating on the surface it will slightly aid geotropism in directing the radicles to the ground.* The Power of Movement in Plants Little squares of card were attached with shellac to one side of the tips of 19 radicles, some of which were subjected to 78o F., and others to a much lower temperature. The Power of Movement in Plants One radicle was deflected only slightly from the perpendicular and from the card; whilst seventeen were plainly deflected. The Power of Movement in Plants Out of the 8 radicles which had been touched with caustic, two alone were not affected, and the marks left on their tips by the caustic were extremely minute. The Power of Movement in Plants In other cases the beans were turned about whilst their radicles were growing, so that they descended nearly vertically on their own smooth, almost flat, broad upper surfaces. The Power of Movement in Plants Their tips are also sensitive to contact, and they are thus excited to bend away from any touching object; so that they resemble in these respects, as far as they were observed, the primary radicles. The Power of Movement in Plants In one case of a radicle, which was growing rather slowly, the root-cap, after encountering a rough slip of wood at right angles, was at first slightly flattened transversely: after an interval of 2 h. The Power of Movement in Plants This occurred chiefly when the first curvature was small, and when an object had been affixed more than once to the apex of the same radicle. The Power of Movement in Plants As the apex of a radicle in penetrating the ground must be pressed on all sides, we wished to learn whether it could distinguish between harder or more resisting, and softer substances. The Power of Movement in Plants Citrus aurantium: two young seedlings: c, larger cotyledon; c', smaller cotyledon; h, thickened hypocotyl; r, radicle. The Power of Movement in Plants The secondary radicles emit tertiary ones, but these, in the case of the bean, are not affected by gravitation; consequently they protrude in all directions. The Power of Movement in Plants Again, certain species of Chaerophyllum and Corydalis produce only a single cotyledon;*** in the former the hypocotyl, and in the latter the radicle is enlarged, according to Irmisch, into a bulb. The Power of Movement in Plants When there was no such absorption and the card was not displaced, it acted well and caused the radicle to bend to the opposite side. The Power of Movement in Plants In 3 days from the time of attachment the terminal portion of the radicle formed a ring or circle. The Power of Movement in Plants There is another occasional movement which must not be passed over: the tip of the radicle, for a length of from 2 to 3 mm., was found in six instances, * 'Arbeiten Bot. The Power of Movement in Plants We believe that there is no structure in plants more wonderful, as far as its functions are concerned, than the tip of the radicle. The Power of Movement in Plants These two sets of cases, especially the first one, prove that the apex of the radicle is sensitive to slight contact and that the upper part bends from the touching object. The Power of Movement in Plants With radicles of the bean, when extended horizontally in damp air, geotropism always conquered the effects of the irritation caused by squares of card attached to the lower sides of their tips. The Power of Movement in Plants Pisum sativum: a radicle extended horizontally in damp air with a little square of card affixed to the lower side of its tip, causing it to bend upwards in opposition to geotropism. The Power of Movement in Plants The thirteenth radicle after 6 h. was slightly curved downwards, but within 21 h. had curved considerably up, and then down again at an angle of 45o beneath the horizon, afterwards becoming perpendicular. The Power of Movement in Plants Therefore, radicles having their tips amputated should be observed in from 12 to 48 h. after the operation. The Power of Movement in Plants At this period the upper part of the radicle is packed within the fruit parallel to the hypocotyl, and the single cotyledon is doubled back parallel to the latter. The Power of Movement in Plants The radicle of the common pea at a point a little above the apex is rather more sensitive to continued pressure than that of the bean, and bends towards the pressed side.* The Power of Movement in Plants Little squares of the card-like paper were next affixed to radicles of the pea at 4 mm. above the apex, in the same manner as with the bean. The Power of Movement in Plants There can, therefore, be no doubt that the apex is highly sensitive to slight contact, and that the upper part of the radicle bends away from the touching object. The Power of Movement in Plants This is the case with the radicles of Sinapis alba, which are plainly apheliotropic; nevertheless, they grow quicker in darkness than in light.* The Power of Movement in Plants Fifteen radicles which had germinated in friable peat were suspended vertically over water. The Power of Movement in Plants Moreover, owing to the hypocotyls being soon developed and becoming arched, the whole radicle is quickly displaced and confusion is thus caused. The Power of Movement in Plants The latter proved unhealthy, and never grew; and the marks on 2 of the 4 slightly curved radicles were excessively minute, one being distinguishable only with the aid of a lens. The Power of Movement in Plants The first and most obvious explanation of the curvature is, that it results merely from the mechanical resistance to the growth of the radicle in its original direction. The Power of Movement in Plants Nearly the same result was observed with the radicles of Zea mays. The Power of Movement in Plants The fact of the apex of a radicle being sensitive to contact has never been observed, though, as we shall * 'Arbeiten Bot. The Power of Movement in Plants Out of 55 radicles experimented on under the proper temperature, 52 became bent, generally to a considerable extent from the perpendicular, and away from the side to which the object was attached. The Power of Movement in Plants Of the three failures, one can be accounted for, as the radicle became sickly on the following day; and a second was observed only during 11 h. The Power of Movement in Plants The result was that all five radicles were bent down, or towards the centre of the earth, after only 8 h. The Power of Movement in Plants That this curvature was due to the action of geotropism during the horizontal position of the radicle, was shown after 4 days, when a new tip had been re-formed, for it then grew perpendicularly downwards. The Power of Movement in Plants The amount of curvature was unaccountably small; but all the radicles which were at all bent, were bent away from the cards. The Power of Movement in Plants Of the eight radicles with their tips immersed in water, seven were plainly curved away from the sliced surfaces after 10 h. The Power of Movement in Plants Square attached on the 21st; on the 22nd slightly curved from the square; 23rd more curved; 25th considerably curved; 27th all curvature lost, and the radicle was now directed perpendicularly downwards. The Power of Movement in Plants It is, therefore, manifest that the apex of the radicle of the oak is highly sensitive to contact, and retains its sensitiveness during several days. The Power of Movement in Plants The growing part of these three radicles increased in 24 h. from 10 mm. to an average of 16.5 mm. The Power of Movement in Plants Thin slips of wood were cemented on more or less steeply inclined glass-plates, at right angles to the radicles which were gliding down them. The Power of Movement in Plants After an additional day the radicle became almost straight. The Power of Movement in Plants Square of card fixed laterally to apex of young radicle; after 9 h. deflection from the perpendicular considerable; after 24 h. deflection reduced. The Power of Movement in Plants These results led us to pursue the experiment, and 18 radicles, which had grown vertically downwards in damp air, had one side of their conical tips sliced off with a razor. The Power of Movement in Plants The radicles in the foregoing cases were measured before their tips were amputated, and in the course of 24 h. they had all increased greatly in length; but the measurements are not worth giving. The Power of Movement in Plants At the same time and within the same jars, 3 radicles of the same age, with squares affixed to one side, were suspended vertically; and after 8 h. The Power of Movement in Plants In these latter cases the irritation from the squares had over-powered geotropism; whilst in the former cases, in which the radicles were extended horizontally, geotropism had overpowered the irritation. The Power of Movement in Plants It is a singular fact that after the ridge has done its work and has escaped from the seed-coats, it is developed into a frill all round the summit of the radicle.* The Power of Movement in Plants Squares of card affixed with shellac: after 24 h. radicles of both curved at about 45o from the perpendicular and from the cards. The Power of Movement in Plants The result was that of the sixteen vertically embedded radicles, four continued for several days to grow straight downwards, whilst twelve became more or less bowed laterally. The Power of Movement in Plants Square of card fixed with shellac to apex of young radicle: after 9 h. deflection from the card and from the perpendicular a right angle; next morning quite straight. The Power of Movement in Plants From these experiments it is clear that the apex of the radicle of the bean is sensitive to contact, and that it causes the upper part to bend away from the touching object. The Power of Movement in Plants One radicle was curved into a semi-circle in so short a period as 6 h. The Power of Movement in Plants Above two dozen beans were thus tried; and when a square of glass or card did not act, it was removed, and a fresh one affixed, this being often done thrice to the same radicle. The Power of Movement in Plants In every one of them the curvature was directed towards the side which had been downwards whilst the radicles remained horizontal. The Power of Movement in Plants Eighteen radicles were tried with little squares of sanded card, some affixed with shellac and some with gum-water, during the few last days of 1878, and few first days of the next year. The Power of Movement in Plants With No. 26, the radicle was almost straight in 48 h. The Power of Movement in Plants These after being touched with thick gum-water, were placed on the tips of eleven radicles. The Power of Movement in Plants It is also always developed with the flat lower side, which, as just stated, forms a part of the radicle, at right angles to it, and in a horizontal plane. The Power of Movement in Plants Of the twelve bowed radicles five became permanently bent into a right angle; the other seven were at first much less bent, and their curvature generally decreased after 24 h., but did not wholly disappear. The Power of Movement in Plants These radicles therefore presented a striking contrast with the 44 above described. The Power of Movement in Plants We may therefore infer that any cause which renders the growth of the radicles either slower or more rapid than the normal rate, lessens or annuls the sensibility of their tips to contact. The Power of Movement in Plants We may therefore conclude from these 15 trials that the radicles are not sensitive to temporary contact, but are acted on only by prolonged, though very slight, pressure. The Power of Movement in Plants So that only 4 out of the 18 radicles were not acted on. The Power of Movement in Plants The five radicles which were rectangularly bent became fixed in this position, and they continued to grow out horizontally in the peat for a length of about 1 inch during from 4 to 6 days. The Power of Movement in Plants Seventeen radicles were thus treated, and were suspended in moist air over water at a temperature of 58o F. They were examined after an interval of 21 h. or 24h. The Power of Movement in Plants Some beans suspended to cork-lids, with their radicles dipping into water, had developed secondary or lateral radicles, which were afterwards kept in very damp air, at the proper low temperature for full sensitiveness. The Power of Movement in Plants A small square of card fixed with shellac to the apex of a young radicle; after 9 h. The Power of Movement in Plants Square of card affixed with shellac: after 8 h. radicle curved at right angles from the perpendicular and from the card. The Power of Movement in Plants Lastly, five other radicles were similarly treated, but were exposed to geotropism during only 45 m. The Power of Movement in Plants A similar square was now affixed laterally with shellac: after 9 h. the radicle was deflected nearly 45o from the perpendicular and from the card. The Power of Movement in Plants A very small piece, less than 1/20th of an inch square, of thin tin-foil fixed with shellac to the apex of a young radicle; after 24 h. no effect. The Power of Movement in Plants A splinter of thin glass gummed to apex, after 9 h. no effect, but it was then found not to be touching the apex of the radicle. The Power of Movement in Plants A little square of thick letter-paper gummed to the apex of a radicle, which after 9 h. was deflected from it. The Power of Movement in Plants It has also been shown in Chapter III. that if a thin slice be cut off one side of the tip of the radicle, this causes the radicle to bend from the sliced side. The Power of Movement in Plants The tertiary radicles, or those emitted by the secondary ones, are not influenced, at least in the case of the bean, by geotropism; so they grow out freely in all directions. The Power of Movement in Plants Most of the squares were fixed to the lower sides of the apex, so that if they acted the radicle would bend upwards; but some were fixed laterally, and a few on the upper side. The Power of Movement in Plants These massive radicles, one of which was above 2 inches in length and .3 inch in diameter at its base, seemed insensible to so slight a stimulus as any small attached object. The Power of Movement in Plants Those of Quercus robur and Zea mays were highly sensitive to contact, as were the radicles of the latter to caustic. The Power of Movement in Plants Accordingly, 30 radicles, with tips amputated for a length of 1.5 mm., were allowed to grow perpendicularly downwards into water. The Power of Movement in Plants Finally, the several co-ordinated movements by which radicles are enabled to perform their proper functions are admirably perfect. The Power of Movement in Plants If they had been acted on like the primary radicle, all the radicles would have penetrated the ground in a close bundle. The Power of Movement in Plants We have seen that if the end of the primary radicle is cut off or injured, the adjoining secondary radicles become geotropic and grow vertically downwards. The Power of Movement in Plants This power must often be of great service to the plant, when the primary radicle has been destroyed by the larvae of insects, burrowing animals, or any other accident. The Power of Movement in Plants The remaining ten radicles were amputated at an angle of about 45o. The Power of Movement in Plants Some influence must therefore be transmitted from the tip along the radicle for this length. The Power of Movement in Plants In order that these movements should be properly displayed, it appears necessary that the radicles should grow at their normal rate. The Power of Movement in Plants After two days slight deflection, which during the next three days certainly increased but never became great; the radicle did not grow well and died on the eighth day. The Power of Movement in Plants These several cases show beyond doubt that the irritation of one side of the apex, excites the upper part of the radicle to bend slowly towards the opposite side. The Power of Movement in Plants Twenty-seven radicles, some young and very short, others of moderate length, were suspended vertically over water, after being thus cauterised. The Power of Movement in Plants The peculiar form of sensitiveness which we are here considering, is confined to the tip of the radicle for a length of from 1 mm. to 1.5 mm. The Power of Movement in Plants With respect to the tips of the secondary radicles, those of Vicia faba, Pisum sativum, and Zea mays were alone observed, and they were found similarly sensitive. The Power of Movement in Plants The contact, however, must be prolonged, for the tips of 15 radicles were rubbed for a short time, and this did not cause them to bend. The Power of Movement in Plants A radicle may be compared with a burrowing animal such as a mole, which wishes to penetrate perpendicularly down into the ground. The Power of Movement in Plants Instead of cutting off the tips, as in the first set of experiments, we next tried the effects of touching horizontally extended radicles with caustic in the manner just described. The Power of Movement in Plants On close examination only a single ungreased radicle could be found which had not become curved towards the sieve. The Power of Movement in Plants Not one of the very numerous ungreased radicles failed to come into close contact with the sieve. The Power of Movement in Plants When radicles with greased tips are left to grow for several days in damp air, the grease is drawn out into the finest reticulated threads and dots, with narrow portions of the surface left clean. The Power of Movement in Plants Thirdly and lastly, radicles when they first protrude from the seed are always geotropic, and plumules or shoots almost always apogeotropic. The Power of Movement in Plants Lengths of radicles reduced to one-half scale, but by an accident the beans themselves not reduced in the same degree. The Power of Movement in Plants With the ungreased radicles the chief seat of curvature is at a distance of not less than between 3.5 and 5.5 mm., and not more than between 7 and 10 mm. from the apex. The Power of Movement in Plants It appears, therefore, at first sight that greasing the tips of these radicles had checked but little their bending to the adjoining damp surface. The Power of Movement in Plants We repeated this experiment, and planted beans with amputated radicles in friable peat, and saw the result described by Sachs; but generally two or three of the secondary radicles grew perpendicularly downwards. The Power of Movement in Plants Now in these four cases, one or more of the secondary radicles, arising from the thickened part just above the wire, had grown perpendicularly downwards. The Power of Movement in Plants The sides of the radicle are also sensitive to contact, but in a widely different manner. The Power of Movement in Plants No explanation has hitherto been attempted of such cases as the foregoing,- -namely, of secondary radicles growing vertically downwards, and of lateral shoots growing vertically upwards, after the amputation of * 'Proc. The Power of Movement in Plants Ten of these secondary radicles, which were directed obliquely downwards, were experimented on with very small squares of card attached with shellac to the lower sides of their tips. The Power of Movement in Plants If therefore the squares acted, the radicles would bend upwards in opposition to gravity. The Power of Movement in Plants The tips of 15 radicles were cauterised with nitrate of silver, and they grew as well as those above described with greased tips. The Power of Movement in Plants If, however, the radicle is pressed by a similar object a little above the tip, the pressed part does not transmit any influence to the more distant parts, but bends abruptly towards the object. The Power of Movement in Plants Thus the destruction of the tip for a length of about 1 mm. prevented the curvature of the greater number of these radicles to the adjoining damp surface. The Power of Movement in Plants The greater number of these radicles were examined after 22 h., and a few after 25 h., and within these intervals they had grown so quickly as to have nearly doubled their lengths. The Power of Movement in Plants In whatever direction the primary radicle first protrudes from the seed, geotropism guides it perpendicularly downwards; and the capacity to be acted on by the attraction of gravity resides in the tip. The Power of Movement in Plants But Sachs has proved* that the secondary radicles, or those emitted by the primary one, are acted on by geotropism in such a manner that they tend to bend only obliquely downwards. The Power of Movement in Plants In our first chapter the movements of the radicles of several seedlings were described. The Power of Movement in Plants Seeds were planted in friable peat at a depth of about an inch in a vertical position, with the end from which the radicle protrudes downwards. The Power of Movement in Plants The cotyledons were still enclosed within the seed-coats; and the short hypocotyl, between the summit of the radicle and the cotyledons, was as yet only slightly arched. The Power of Movement in Plants With Ranunculus ficaria two cotyledons are never produced, and here one of the secondary radicles is developed at an early age into a so-called bulb.** The Power of Movement in Plants This was shown by the tracks often being alternately a little broader and narrower, due to the radicles having alternately pressed with greater and less force on the plates. The Power of Movement in Plants Seven radicles were extended horizontally for an hour, instead of 1 h. The Power of Movement in Plants Beans thus arranged, surrounded by damp sand, lifted up a quarter of a pound in 24 h. after the tip of the radicle had entered the hole. The Power of Movement in Plants How much of the drawing down and burying of the hypocotyl of Opuntia basilaris was due to the contraction of this part and how much to that of the radicle, we did not observe. The Power of Movement in Plants With the other pincers the radicle escaped still further out of the hole; and the weight required to open them to the same extent as had been effected by the radicle, was only 600 grams. The Power of Movement in Plants With these facts before us, there seems little difficulty in understanding how a radicle penetrates the ground. The Power of Movement in Plants In the second, the curvature increased during two days and then decreased. the third radicle became permanently bent, so that its terminal part made an angle of about 45o with its original vertical direction. The Power of Movement in Plants The radicle of a seedling was cut off, as it was completely decayed, and the two now separated cotyledons were planted. The Power of Movement in Plants With a greater weight the radicles themselves always became bent on the one unguarded side; but this probably would not have occurred if they had been closely surrounded on all sides by compact earth. The Power of Movement in Plants The fissure which was at first quite closed, was now open to a width of 4 mm.; as soon as the radicle was extracted, it immediately closed to a width of 2 mm. The Power of Movement in Plants Secondary roots sometimes spring from the lower surface of the peg, which thus seems in all respects to partake of the nature of the radicle. The Power of Movement in Plants L, side of bean which lay on the peat, whilst geotropism acted on the radicle. The Power of Movement in Plants Two radicles in damp sand were allowed to grow through these holes. The Power of Movement in Plants The nutriment within the cotyledons is then quickly transferred to the hypocotyl or radicle, which thus becomes developed into a fusiform tuber. The Power of Movement in Plants After six days the stick and bean were dug out of the damp sand, and the radicle was found to be much enlarged above and beneath the hole. The Power of Movement in Plants If this escape and flattening could have been prevented, the radicle would probably have exerted a greater strain than the 3 pounds 4 ounces. The Power of Movement in Plants It is therefore remarkable that Sachs, who experimented on many radicles with their tips amputated, found extremely disordered growth to be the usual result. The Power of Movement in Plants Their petioles are completely confluent, forming a tube which terminates downwards in a little solid point, consisting of a minute radicle and hypocotyl, with the likewise minute plumule enclosed within the base of the tube. The Power of Movement in Plants The petioles are clothed with root-hairs like those on a true radicle, and they likewise resemble radicles in becoming brown when immersed in a solution of permanganate of potassium. The Power of Movement in Plants In one specimen which was closely observed, the petioles in 7 days after their first protrusion attained a length of 2 ½ inches, and the radicle by this time had also become well developed. The Power of Movement in Plants |
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