Chlorophyll breaks down and is replenished all summer long. As daylight hours shorten, however, veins that bring water and nutrients to the leaf gradually close off.

　　整个夏天，叶绿素不断分解，然后又被补足。但是当日照时数缩短的时候，为叶子带来水分跟营养的叶脉会逐渐关闭。