On the Life-History of Vanilla planifolia

Abstract

1. In the orchid Vanilla planifolia the microspores do not remain united to form compound grains, massulae, or pollinia, but lie free inside the anther. The pollen grains are shed at the two-celled stage. 2. The nucellus shows a greater development than in most other orchids, and the nucellar cells at the chalazal end persist even in the mature seed. 3. The outer integument consists of four to six layers of cells which persist in the seed. In other orchids only the outermost layer is recognizable in the seed. 4. The inner integument is also two-to three-layered and, although flattened and crushed, remains distinguishable for a long time. 5. The embryo sac arises from the chalazal cell of a row of three cells, consisting of a micropylar undivided dyad cell and two megaspores. After the four-nucleate stage, the two chalazal nuclei do not divide further, resulting in a six-nucleate embryo sac. 6. Double fertilization takes place normally, but, since there is no lower polar nucleus, the primary endosperm nucl...