DEVELOPMENT OF NORMAL AND SEEDLESS ACHENES IN CICHORIUM INTYBUS (COMPOSITAE)

Cross- and partially cross-pollinated capitula of Cichorium intybus (Compositae, Lactuceae) were examined for a study of normal and seedless fruit development respectively. Embryos develop according to the Asterad pattern, and the free-nuclear endosperm becomes cellular 15–17 hrs after pollination. A zone of disorganized cellular material surrounds the embryo sac at anthesis, and, in normal achenes, this zone expands as the seed develops. Initially the developing seed elongates and comes into contact with the top of the ovary by 48 hrs. In contrast to this pattern, the ovule in developing seedless achenes degenerates within 72 hrs. Irregularities, such as an abnormally proliferating endothelium, embryo formation without endosperm, and endosperm formation without an embryo often accompany this degeneration. Differentiation of the pericarp in seeded achenes begins between 48 and 72 hrs, starting at the apex and proceeding basipetally; in seedless fruits the process is similar though initiated somewhat later. The normal pericarp at maturity exhibits a pigmented exocarp, a broad mesocarp of thick-walled lignified cells, and a tenuous endocarp. In seedless achenes the fruit coat is similar except that the exocarp is colorless and the cells of the mesocarp are relatively small.