双子叶植物出土幼苗根茎转变区维管组织发育动态

关于根茎初生维管系统之间的连接以及与子叶的关系，在文献中已有广泛的论述，有过各种不同的解释。大部分早期关于根茎转变区的文献研究的是初生组织已完成发育的幼苗。这些研究者认为转变区域是根和茎这两种轴器官之间维管组织发生转变、相互连接的区域。但由于茎中的初生维管组织可以认为是叶迹及叶迹的延伸的综合，转变区域应被看作是轴维管系统与叶迹维管系统之间的连接。因此，转变区的研究必须说明根维管系统与最早的真叶叶迹之间的关系。通过对北乌头和大豆胚胎及幼苗维管组织的解剖学研究，本工作显示在出土萌发的双子叶植物中，初生维管组织在根-下胚轴-子叶中形成一连续系统，并完成根与子叶叶迹之间的维管组织过渡转变。而上胚轴中的维管组织是位于根-下胚轴-子叶上方独立形成的第二维管系统。上胚轴中维管组织的分化起始于第一真叶叶迹基部，向上分化进入叶片，向下进入胚轴并在子叶节下方与根-下胚轴-子叶维管系统相连接。真叶叶迹的木质部与下胚轴中靠近韧皮部的后生木质部或次生木质部连接。根与上胚轴之间不存在维管组织的过渡、转变，而只是在同样发育方向的组织中有一种直接的简单的连接．

Vascular development in the transition region of dicotyledonary epigeal seedlings

Seeds and developing seedlings of Aconitum kusnezoffii were anatomized to examine vascular development in the root hypocotyl transition region. The seedlings of Glycine max used to study the connection of the xylem from root to shoot. The germination of the both plants is epigeal. The change in orientation of vascular development is accomplished abruptly below the cotyledonary node. The primary vasculature of the root hypocotyl cotyledon is in continuation whereas the epicotyl vasculature is connected through the later formed vascular elements. The study supports Esau's (1965) view that the epicotyl is superimposed over the root hypocotyl cotyledon unit forming two independent units. There is no transition between root and epicotyl of dicotyledonous seedlings with epigeal germination, whereas only having a directly simple connection between the tissues with the same radially developmental direction.