After a few days, the sides of the first layer, called the primary cell wall, stiffen, pushing cell growth in one direction and causing the fiber to elongate.

几天后，第一层细胞壁，亦称为初生细胞壁，变硬，向一个方向推动细胞生长，从而使纤维被拉长。

Powered by non rechargeable primary cells, although it was capable of reaching four miles per hour, the limitations of battery technology at the time made it impractical.

它由不可充电的原电池供电，虽然能够达到每小时四英里，但当时电池技术的限制使其不切实际。

Now, even though the idea of a battery-powered vehicle was to revolutionize people's lives for the better, primary cell batteries (that's the " use once and toss" kind) weren't the way to go for obvious reasons.

现在，虽然电动汽车的想法是为了让人们的生活变得更好，但显而易见，原电池（即用即弃的那种）并不实用。