Studies on the Stolon Development in the Potato Plant : I. The orientation of the axillary shoot growth in the potato seedlings

Many scientists study the tuberization of potato plants from the point of view of the environments and the plant hormones. The tuberization is also recognized as the result of two separate processes, stolon formation and tuberization of the stolons. The stolons are the axillary shoots which normally arise from the underground nodes. In this paper, stolon formation was studied using the potato seedlings from which axillary shoots arose from the aerial nodes. The results were summarized as follows. 1. Three types of orientation of the axillary shoot growth in the potato seedlings were recognized:the axillary shoots grown downwards at the lower nodes, those grown horizontally at the middle nodes and those grown upwards at the upper nodes. 2. The downward growth of the axillary shoots at the cotyledonal node was a consequence of the increased upper epidermal cell number and the cell length of the axillary shoots. On the other hand, the upward growth of the axillary shoots at the 7th node was a consequence of the increased lower epidermal cell number. 3. It is suggested that the orientation of the axillary shoots was controlled by the shoot apex with some younger leaves. Whenever the excision of the shoot apex was earlier or later, the axillary shoots turned upwards to become the leafy shoots. However, the change of the orientation to upwards was accelerated by the earlier excision of the shoot apex. 4. It was recognized that the decapitation of the shoot apex caused the axillary shoots to turn upwards and show the leafy shoots. However, if IAA and IAA+KIN were applied to the cut surface, the upper-most axillary shoots grew the downward and stoloniferous shoots such as intact ones. Thus it was suggested that there was a evident relationship between the endogenous auxins in the shoot apex with some younger leaves and the growth pattern of the axillary shoot.