Abstract
1. Experiments were carried out to examine the effects of light intensity during the growth upon the branching in pea. The varieties tested were GW for the strain of arvense and Usui and World Record for that of hortense.
2. The plants in the field or in pots were shaded from emergence to harvest under cheese-cloth tunnel of synthetic textile (“Vinylon”). In some experiments in the latter half of the growing period the cover was removed and further in a supplementary experiment the row was mulched with straw to restrict the quantity of light the young plants receive. The light intensity in the tunnel was controlled by varying the number of cheese-cloth layers.
3. In all the varieties tested, shading accelerated the internode elongation in the main stem. The trend was most remarkable in the variety GW.
4. In shaded plants, branching at lower nodes of the main stem was arrested while the production of upper branches stimulated. The inhibition of the development of lower branches was enhanced as the shading became heavier. The effect of restricted light intensity was quite as remarkable in the short-term shading during the early growth stage as in the shading throughout the growing period.
5. The influence of shading on the subsequent growth of developed branches varied from one experiment to another. Temperature, varietal difference in branching and other unidentified factors might be herein involved.
6. In the previous reports, the authors have made it clear that long photoperiod, high temperature and application of gibberellic acid are favourable for the development of upper branches and inhibitory to the branching at lower nodes. In the present experiment, shading has proved itself to be another factor which demonstrates the same effect on the branching in pea.
The current experimental data have afforded the evidence that these four factors are all potent in raising the content of auxin and/or gibberellin or in enhancing their activity in higher plants. As the consequence and in fact, these facts are in common in encouraging the internode elongation of the main stem of pea plants. Associating with these connections, a brief discussion was developed.
7. The foregoing results suggest the important role of light intensity in the morphogenesis of pea plants and offer data for the practical considerations in the culture of this crop.
