A Comparison of the Effects of Green Light and of Red Light on the Simple-leaf Development of Intact and Decapitated Bean Plants.

Increasing effort is being directed to the study and interpretation of both quantitative and qualitative effects of light on plants and a number of investigators have emphasized the inadequacy of present information. Any satisfactory description of the ways in which light may affect the form and growth of plants may be anticipated only as a result of many small contributions by various investigators using varied angles of approach. At the Richmond meeting in 1938 a report was made on experiments in which white potatoes, beans, and strawberry plants were grown for some weeks in continuous illumination under green fluorescent mercury tube grids. The point of seeming interest at that time was that while the plants made fair growth, no starch was found at any time in the leaf mesophyll, though it was abundant in the guard cells. That starch was abundant under such conditions afforded supporting evidence that the guard cells were without plasmodesmata. The results suggested the possible usefulness of this tvpe of illumination when stomata counts were desired (figure 1), since upon clearing with alcohol and staining with IKI solution the stomata became very prominent. The relations of quality of light to stomatal opening and to translocation were obscure and no interpretation of the plant response under this illumination was advanced. During 1941 two sets of tests with this illumination were carried out. In the first of these the growth of the simple leaves of beans (Phaseolus vulgaris L.) under continuous green light was compared with the growth under continuous red light from neon tube grids. All plants were started in April in cans of soil in a greenhouse and were transferred to the experimental conditions at a time when the simple leaves were about half expanded and small compound leaves were just beginning to expand. Sixteen or more plants were placed under green and red tube lights in a chamber in which a temperature of 200 C. was maintained. Other groups of plants were placed under similar lights in a laboratory in which room temperatures of about 250 C. prevailed. Under each set of conditions half of the plants of each lot were decapitated just above the simple leaves. In addition to the plants under green and red tube lights a further set was placed under green G. E. fluorescent lamps at room temperature. Following one week of continuous illumination the simple leaves were measured. The results obtained have been brought together in table I. 677