初中植物学课本第四章(叶)第一节(叶的形态)中,在讲述变态的叶时指出,仙人掌的刺“是由叶变成的,叫做叶刺。仙人掌的叶全部变为叶刺”。高中生物学课本第七章第一节里也讲到“仙人掌的叶变成了刺”。几位读者来信对此提出了疑问。我们曾把信转给北京大学李正理教授,他也认为这的确是一个值得说明澄清的问题。人们只要留心观察仙人掌科植物的生长情况,不难看到,许多仙人掌科植物茎尖的幼嫩部分,在长出新芽的过程中,有绿色的小叶片出现,在叶腋内萌生出一个或几个刺,有的还有一 In the first section (leaf form) of the fourth chapter (leaf) of the junior middle school botany textbook, when describing the metamorphic leaves, it is pointed out that the thorns of the cactus are changed from leaves to leaf thorns. The leaves of the cactus all become leaves. thorn“. The first section of the seventh chapter of the high school biology textbook also states that ”the leaves of a cactus become a thorn." Several readers questioned this letter. We once transferred the letter to Professor Li Zhengli of Peking University. He also believes that this is indeed a question worthy of explanation. As long as people observe the growth of cacti plants, it is not difficult to see that in the young shoots of many cacti plants, green shoots emerge during the emergence of new shoots, and one or more of them emerge in the leaves. Thorn, there are still one