Skoog ('34) has stated that the inhibition of growth in Avena (oat) and other seedlings, caused by x-rays, is attributable to the destruction of a growth-promoting substanceauxin. Navez ('33) has reported that twice as much auxin is produced in light-grown lupinus seedlings as in darkgrown. This greater amount of auxin is apparently present as an excess, since growth is not markedly different in the two sets of seedlings.
If these findings be generally true, then small doses of
x-rays might be expected to destroy only the excess auxin in light-grown seedlings, without having any pronounced effect upon the early growth after x-ray treatment. The light-grown seedlings would, then, be less sensitive to x-rays than the dark-grown. This, and related questions will be considered in the present paper.
Methods
The wheat seedling, Triticum aestivum L. (T. vulgare Villars) was used in this study. Seeds were soaked for an hour in tap water, in the diffuse light of the laboratory. They were then put into glass moist chambers, one transparent and one painted black, and placed 50 em. under a 75-watt daylight bulb in an incubator kept a t 26" C. The dark chamber was wrapped in several layers of black paper and was not directly under the light. The temperature in the two 69