Epigeal Germination in the Leguminosae

Abstract

1. Epigeal and hypogeal germination in Phaseolus vulgaris and P. multiflorus, respectively, constitute a pair of inter-specific genes. By germinating the seeds of the garden bean and the scarlet runner (a pole bean) in various positions, it was found that the hypocotyl of the latter is not at first geotropically sensitive but may grow out in any direction. This is supported by the recent finding that the hypocotyl in seedlings of P. vulgaris does not contain diffusible auxin. On the other hand, the primary root which develops from the tip of the hypocotyl is always positively geotropic. There is no evidence as to why the zone of growth is above the attachment of the cotyledons in one species and below it in the other, but distribution of auxin in the very young seedlings is presumably involved. 2. A survey of the Leguminosae as regards the methods of germination shows that the Mimosoideae and Caesalpinioideae are apparently all epigeal, whereas in the Papilionatae some tribes are epigeal, some hypogeal, both types of germination being found within the Trifolieae and Phaseoleae. In the evolution of the order the transition from one type to the other must have occurred several times. Erythrina monosperma and E. suberosa may form a pair of species like P. vulgaris and P. multiflorus, but wide variation in length of hypocotyl in different species and other intermediate conditions indicate that in some cases several genes are probably involved in the transition. There is need for much work on the genetics of cotyledon size and shape in the Leguminosae.