節網維管束ノ起原ト構造

たうもろこしノ維管束解剖 第四報

抄録

By means of the serial sections of the microtome, the horizontal bundles, forming the nodal plexus, have been studied with reference to their origin and anatomical feature. The nodal plexus, i. e. the inextricable tangle of the horizontal bundles is found between the vertical bundles in the fundamental tissue of the nodal region. It consists of the imperfect concentric vascular bundles, connected together into a complex network, the phloem being surrounded by the xylem.
In the mature stem, the nodal plexus is connected with the outermost peripheral bundles (stem cylinder) and often with the compound bundles which are close to the former. The large leaf traces are never connected with the nodal plexus, at least, at the node where they detach from the leaf and enter into the centre of the stem. The nodal plexus has no primary relation in its origin to the vascular supply for the axillary bud and the adventitious root, because it is often differentiated even in the budless or rootless node.
At the apex of the growing shoot, the large leaf traces are differentiated at first as the procambial strands, but the horizontal procambium is not yet observed, and all the tissue are still in the state of the primary meristem, each cell of which dividing in a random direction. Soon after the differentiation of the protoxylem is initiated in the vertical procambium situated at the centre of the stem, the horizontal procambial strands become suddenly differentiated among the primary meristem (fundamental meristem) of the nodal region, and afterwards the nodal plexus is constructed from them. The horizontal procambium seems to be differentiated simultaneously both in the centre and in the periphery of the stem, while the differentiation of the vertical procambium proceeds from the centre towards the periphery of the stem. Therefore, the interval of the time between the differentiation of the horizontal bundles and of the vertical ones, is smaller in the periphery than in the centre of the stem. From this fact, it is understood that the horizontal bundles of the nodal plexus are more closely connected with the vertical bundles of the periphery of the stem than with those of the centre.
The results of the present study of the maize plant lead to the conclusion as follows: the horizontal bundles, forming the nodal plexus, are a little behind the vertical bundles in the time of their initial differentiation, yet they originate as the procambial strands directly from the fundamental meristem, not from the fundamental tissue by means of a recrudescence of its meristematic activity; and further the primary connexion, in the strict sense, is not found between the nodal plexus and other bundles such as the large leaf traces or the bundles supplied for buds or roots.