在学习生物课进行“考察根系分布的规律”活动时,你可能发现大豆、豌豆等豆科植物的根系有很多瘤状突起———根瘤(图1左),而其他作物如水稻、小麦等则没有(图1右)。为什么豆科植物根系会形成根瘤呢?在18世纪中叶以前,人们不知道根瘤形成的原因,当有显在18世纪中叶以前,人们不 In the “Learn the laws of root distribution” activity in the Learning Biology class, you may find that the roots of soybeans, peas, and other legumes have many nodules—root nodules (left in Figure 1). Other crops such as rice, wheat, etc. There is no (Figure 1 right). Why do legume roots form nodules? Before the middle of the 18th century, people did not know the cause of root nodule formation. When it appeared in the middle of the 18th century, people did not