Studies on the branching in Pisum sativum L. V.

1. To elucidate possible relationship between branch development and elongation of related stem internodes, length of each internode of the main stem and length of branches were measured at regular intervals.2. In general, each internode of the main stem except some basal ones continued its elongation for 6-8 days at higher temperatures and for 15-20 days at low temperatures. Before the termination of growth of an internode, the next new internode began to grow out. The internode elongation was more active in upper internodes than in lower ones.3. In shaded plants and in plants treated with GA, elongation of upper internodes was very remarkable, but that of two or three basal internodes was only slightly affected by the treatment.In these plants, development of lower branches was poor and their subsequent elongation was considerably arrested, in particular, after initiation of enhanced elogation in upper internodes.4. In plants treated with TIBA, the stem internode elongation was perfectly arrested for 2-3 days. Then, despite the subsequent restoration of internode growth, a remarkable elongation of lower branches was observed after this period of stem growth retardation.5. It may be concluded from the data presented in this report that there is no morphological correlation between development off lower branches and elongation of relevant stem internodes. On the other hand, a marked influence of upper internode elongation on branch formation was confirmed. Plants with active elongation in upper intenodes had poor branches at lower nodes and vigorous branches at upper nodes, whereas plants whose upper internode elongation was in some way suppressed had active development of lower branches and restricted production of upper branches.6. It was revealed that, notwithstanding the almost perfect similarity in the pattern of internode growth between the control and TIBA-treated plants, elongation of branches was far more active in the latter. This means explicitly that some physiological processes are operating here other than simple morphological growth correlation.