【摘要】 通过对甜研四号幼苗下胚轴连续切片的观察,可见甜菜根—茎过渡区发生于下胚轴的较上部,大约位于子叶节下方约0.3—0.6cm处。下胚轴的中、下部具有根的结构特点。这种变化是急骤的。其变化过程如下: 外始式、二原型的初生木质部纵裂为二,中央出现髓。以后, 二分裂后的后生木质部各自向相反方向侧向扩展,直至由外始式的初生木质部转变为内始式的初生木质部。 与初生木质部交互排列的二初生韧皮部各自延伸并分离,其距离逐渐增大,而来自不同韧皮部的小束,其距离逐渐减少。 各小束韧皮部与已成为内始式的初生木质部相结合,形成四束外韧维管束,其中两两相靠,但不融合。最后,在每一子叶中形成一个具有二小束外韧维管束的子叶迹。 在离子叶节约0.2—0.3cm处,真叶叶迹出现,并逐渐发生变化。更多还原

【Abstract】 The slices of hypocotyl of seedling (Tian Yian 4) Were observed continuously, and found that the root stem transition zone of sugar teet occurs in the upper part of hypocotyl, it is located about 0.3-0.6cm under the cotyledon node. The middle and low parts of hypocotyl with the characteristic of root-like structure. The changes occur rapidly. The processes of the changes are as follows:At 1st, the primary xylem which is exarch and diarch divides into two parts longitudinally. And a pith has been formed in the centre. After division, the metaxylems are laterally extended in opposite direction respectively, until the primary xylem is turned from the exarch into the endarch condition.The groups of primary phloem alternating with the primary xylem extend and seperate each other. The distance between two parts of the separeted phloem is increased gradually, but the distance is decreased gradually from various boundles.Each boundles of the phloem is connected with each boundle of the endarch primary xylem to form four collateral boundles, in which two couple of boundles are near contacted with each other, however, they are not mixed together. Finally, they become a cotyledon trace with two collateral boundles in each cotyledon.At 0.2-0.3cm below the cotyledon node, the folial traces of true leaf appeared and changes have taken place gradually.更多还原