both upper and lower epidermal layers

例句：

1. 1. The plant's roots penetratethe soil to reach both upper and lowerepidermal layers.
   植物的根深入土壤，到达上下表皮层。
2. 2. The scientiststudied the structure of the plant'sepidermal layers in detail.
   科学家详细研究了植物表皮层的结构。
3. 3. The researcher found that the plant's epidermal layers play a crucial role inits growth and development.
   研究者发现，植物的表皮层在生长和发育中起着至关重要的作用。