【英语时差8,16】秋季落叶的奥秘-下

 Because chlorophyll is the chemical responsible for making leaves green, its absence allows chemicals such as carotinoids, xanthophylls, and others to give leaves their orange, yellow, and various other colors. As trees stop producing chlorophyll, they start producing sugars and amino acids that act as a sort of antifreeze to protect plants from the winter cold. Meanwhile, nutrients¹ drain from the leaves, through the stems, and eventually into the roots, where they remain for the winter. When the nutrients have left the leaves, all that remain are cell walls and nutrient-depleted protoplasm. Since all that now holds leaves to a tree are brittle², dry, and easily broken veins³, a gust⁴ of wind is enough to tear leaves from the tree and send them fluttering to the ground. When dead leaves break away, they leave behind waxy⁵ cells that form a small bud called a bundle scar. When warm weather returns, each scar will give rise to a newly born leaf.

1 nutrients   

n.（食品或化学品）营养物，营养品( nutrient的名词复数 )

参考例句：

• a lack of essential nutrients 基本营养的缺乏
• Nutrients are absorbed into the bloodstream. 营养素被吸收进血液。 来自《简明英汉词典》

2 brittle   

adj.易碎的；脆弱的；冷淡的；(声音)尖利的

参考例句：

• The pond was covered in a brittle layer of ice.池塘覆盖了一层易碎的冰。
• She gave a brittle laugh.她冷淡地笑了笑。

3 veins   

n.纹理；矿脉( vein的名词复数 )；静脉；叶脉；纹理

参考例句：

• The blood flows from the capillaries back into the veins. 血从毛细血管流回静脉。 来自《简明英汉词典》
• I felt a pleasant glow in all my veins from the wine. 喝过酒后我浑身的血都热烘烘的，感到很舒服。 来自《简明英汉词典》

4 gust   

n.阵风，突然一阵（雨、烟等），（感情的）迸发

参考例句：

• A gust of wind blew the front door shut.一阵大风吹来，把前门关上了。
• A gust of happiness swept through her.一股幸福的暖流流遍她的全身。

5 waxy   

adj.苍白的；光滑的

参考例句：

• Choose small waxy potatoes for the salad.选些个头小、表皮光滑的土豆做色拉。
• The waxy oil keeps ears from getting too dry.这些蜡状耳油可以保持耳朵不会太干燥。