Some Effects of Plant Growth-Regulators on Seed Germination and Seedling Development

1. In studies in moist chambers, 2,4-dichlorophenoxyacetic acid was found to delay germination and to cause abnormalities in the seedling development of twenty-two broadleaf and cereal species. Isopropyl-N-phenylcarbamate was less effective than four chlorophenoxyacetic acids in reducing growth of seedlings of maize. 2. 2,4-dichlorophenoxyacetic acid and 2-methyl-4- chlorophenoxyacetic acid applied to the soil prevented the germination of broadleaf species at rates which stunted cereals but did not prevent establishment. Isopropyl-N-phenylcarbamate prevented the establishment of cereals at rates which had no effect upon broadleaf species. Buckwheat, a dicotyledonous species, responded like a cereal. 3. Mixtures of chlorophenoxyacetic acids with isopropyl-N-phenylcarbamate inhibited the development of seedlings of both broadleaf and cereal species and hence have promise as general herbicides, but they gave no evidence of complementary action of the two types of compounds. 4. The general lack of specificity of 2,4-dichlorophenoxyacetic acid in inhibiting the germination of seeds of twenty-two different species may have practical applications in weed-control programs.