Growth-Promoting Substance and Illumination.

The presence of growth-promoting substance-auxin (Kogl and Haagen Smit, 1931)-in the tip of the coleoptile of Avena has been proved repeatedly by several investigators (Went, 1928; Dolk, 1931), through its effect on elongatiQn of shoots of species related or not to the one used as source of supply. Most work has been done with etiolated seedlings, or at least with seedlings grown in the dark for the greater part of their active growth. This obviously must be done in order to prevent conflict with the phototropic reactions particularly marked in Avena, one of the most widely used species for this type of experiment. In the course of experiments on the resistance of auxin to light, I have had occasion to compare the production of the substance in plants grown under the same conditions of temperature, moisture and substrate but differing as to the presence or absence of light. Brief indication of a possible favorable effect of light on the yield of growth-promoting substance from Rhizopus suinus is found in a recent paper by Thimann and Dolk (1933). Germination of Lupinus albus seeds was done on sawdust, after a 10 hours' soaking in sterile distilled water, in incubators at 250