Long and Kersten (1936) found small doses of soft X-rays (long wave length) stimulate the growth of plants from seeds. Moore and Haskins (1933) observed retardation of growth of plants grown from seed irradiated with X-rays from the Coolidge tube which emanates a large proportion of hard X-rays (short wave length). Skoog (1935) has shown that 92 per cent (1000 units per cc.) hetero-auxin (B-indolyl acetic acid) in water is inactivated by hard X-rays filtered through lead, steel, and aluminum filters after exposure of 100 minutes, when the X-ray tube was operated at 3-4 milliamperes at 900 kilovolts. This raises the question as to whether "hetero-auxin" which is inactivated by hard X-rays is also inactivated by soft X-rays.
Proceedings of the Iowa Academy of Science
©1942 Iowa Academy of Science, Inc.
Turrell, F. M. and Kersten, Harold
"A Qualitative Study of the Effect of Soft X-Rays on the Activity of B-Indolyl Acetic Acid as a Growth substance,"
Proceedings of the Iowa Academy of Science, 49(1), 139-143.
Available at: https://scholarworks.uni.edu/pias/vol49/iss1/16