MORPHOLOGICAL DEVELOPMENT OF THE NORTH-AMERICAN PAWPAW DURING GERMINATION AND SEEDLING EMERGENCE

The North American pawpaw [Asimina triloba (E.) Dunal], a temperate me mber of the Annonaceae, is a deciduous woody tree with ornamental valu e and has merit as a fruit crop. Anatomical studies of paw-paw seed re vealed a small, Linear embryo that does not change in length during co ld or warm stratification. Radicle and cotyledon growth from planting until radicle protrusion was concurrent and at about the same rate, Co tyledons grew through a specialized channel of cells Extending above t he cotyledon tips, but never emerged from the seed, The extended perio d of time required for the development of the cotyledons delayed seedl ing emergence more than 50 days. The cotyledons appear to be haustoria l and translocate storage material from the endosperm to the growing e mbryo. At the time of epicotyl elongation, the radicle and developing root system were well developed and comprised 81% of the seedling biom ass, Seedling development could be divided into four distinct stages, including radicle protrusion, hypocotyl emergence, epicotyl elongation , and seedcoat abscission.