Plant Growth Substances Discussed at Madison A STAFF REPORT S C I E N T I S T S from all sections of the United States as well as several foreign countries were attracted to the University of Wisconsin Sept. 1 to 7 for two symposia dealing with the nutrition and growth of plants. Through the interest of the university's committee on growth substances research in bringing together people interested in both fundamental research and applications, there was organized a symposium on plant growth substances, held Sept. ô to 7. The history of the field was reviewed in papers by A. J. Haagen-Smii m d F. ΛΥ. Went, both of the California Institute of Technology. The importance • >!' the discovery of auxin as a plant hormone and its isolation were stressed is being a signal step loading to the development of several materials im portant Today, as 2.4-diphenoxyacotic icid. naphthalene acetic acid, and others. The structure and function of the synthetic auxins wore reviewed by K. V. Thimann. Harvard University, who of fered the suggestion that auxins may bo generally viewed as malonie acid deriva tives: substances in which a ring has taken the place of one of the carboxyl groups in a dicarboxylie acid. H e con tinued with the postulation that succinic dehydrogenase or similar enzymes may be critical for plant growth and these may be protected from inhibition by the auxins. H e cited evidence of the im portance of four-carbon acids in plant growth. In another paper he reported work showing that four-carbon acids are accumulated during plant growth inhibi tion and used up during growth. The effects of growth substances on respiration were reported from two sources. G. S. Avery, Brooklyn Botanic Garden, showed that some seedlings have enhanced carbon dioxide output under the effect of 2,4-D. There was stimula tion at low concentrations with inhibi tion at high. The selectivity of this
compound was shown by comparison on oats and peas, the former requiring about 1,000 times the quantity to yield an equal effect, supporting the observa tion that the monocotyledons are mark edly less affected. F. G. Smith, Iowa State College, showed that quantities considerably greater than those required for growth stimulation cause inhibition • >f respiration and this may be significant in herbicidal action. It was noted, how ever, that herbicides also may cause
