Changes in the cotyledons of Cucurbita maxima during germination. I. General characteristics

Various structural and physiological changes in squash cotyledons were followed as a function of germination time. Temperature, to which squash plants are very sensitive, was kept constant at 31 °C but light conditions were varied.In light-germinated plants (16 h light/day) the cotyledons changed from storage organs to greatly enlarged photosynthetic leaves, within 5 days. Incorporation of major amounts of thymidine-2- 14 C throughout the cotyledons occurred only during the enlargement phase.Dark-germinated plants, in which the cotyledons enlarged very little, produced a long, stout hypocotyl. No major incorporation of thymidine-2- 14 C into the cotyledons occurred, suggesting that little cell division occurs in the cotyledons of dark-germinated squash plants.Fresh- and dry-weight changes in the cotyledons were consistent with the changes in morphology of light- and dark-germinated plants. The cotyledons of plants which were dark-germinated for 6 days and then placed in 16 h light per day did not reach the fresh weight per cotyledon or dry weight per cotyledon level attained by cotyledons from plants germinated, from the beginning in 16 h light per day.