Abstract
In 1937 Billings1 published a paper on the reproductive cytology of angiosperms, illustrated by Isomeris arborea. His observations may be summarized as follows: (1) this plant is a haploid with a complement of 17 chromosomes; there is no true meiosis or syngamy; (2) the megaspore mother cell functions directly without producing the usual megaspores; (3) the mature embryo sac is 3-nucleate, consisting of two synergids and an endosperm nucleus, a true egg being absent; (4) there is no fertilization; (5) the endosperm begins as free nuclear, but soon a part of it becomes differentiated into multinucleate vesicles or nodules; and (6) the embryo arises as a direct outgrowth from one of the endosperm nodules.
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