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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。
By observing the continuous hypocotyls of sweety seedlings, we found that the beetroot-stem transition occurred in the upper part of the hypocotyl, about 0.3-0.6cm below the cotyledonary node. Hypocotyls in the lower part of the root with the structural characteristics. This change is abrupt. The process of change is as follows: external, two prototype of xylem longitudinal split two, the central emergence of pulp. Later, the late-split second-genus xylem flanked each other in the opposite direction until it was transformed from the primordial xylem to the intial xylem. The two primary phloem arranged alternately with primary xylem extended and separated each other, the distance between them gradually increased, and the distance from the phloem of different phloem decreased gradually. Small bundles of phloem and has become the initial type of xylem combined to form four bundles of external vascular toughness, of which two or two rely on, but not fusion. Finally, a cotyledon is formed in each cotyledon with two smaller bundle bundles of external vascular bundles. Leaves 0.2-0.3cm at the leaf, true leaves appear, and gradually changes.