Growth-Promoting and Growth-Retarding Substances in Pollen from Diploid and Triploid Apple Varieties

1. The material for the present study was pollen from one diploid and two (in some cases three) triploid apple varieties. 2. In the triploid varieties the number of pollen grains per anther was 72-88% lower than in the diploid. 3. The percentage of germination was much higher in pollen from the diploid variety than in pollen from the triploids. In no case was germination improved by the addition of indoleacetic acid. 4. A neutral and an acid growth-promoting substance and a neutral growth-inhibitor (Avena test) were obtained by ether extractions of dried pollen. (Extracts were collected for assay from a given sample of pollen after 1, 2, 24, and 168 hours, fresh ether being added each time.) 5. After 1 and 2 hours the growth-promoting and the growth-retarding activities of the extracts were almost equal (table 5). Later on, however, an excess of growth-promoting activity developed. The total excess of growth-promoting over growth-retarding activity was considerably less in pollen from the diploid than in pollen from the triploids. 6. The results of the determinations of growth-promoting and growth-retarding substances in the pollen grains do not explain the differences in germinability and poilinating value of pollen from the diploid varieties. 7. From determinations of the weight of the material extracted from the pollen grains, it is concluded that the growth inhibitor is more active in the Avena test than anemonin and parasorbic acid.