It may reflect an evolutionary process from no-nodules legume plants to nodules legume plants. 豆科植物的表皮细胞外切向壁厚度似乎能够反映豆科植物从不结瘤到结瘤的进化过程。
The outer tangential wall of no-nodules legume plants epidermal cells is thicker and darker than that of nodule legume plants. 非结瘤豆科植物的根表皮细胞外切向壁的厚度比结瘤豆科植物的要厚，颜色也较深。
