The Ovule

Abstract

Of the first classical microscopists, Grew (1671) and Malpighi (1675), the latter was so impressed by the analogous processes of seed maturation and fetal development that he applied the terms “amnion” and “chorion” to the envelopes of the ovule. Grew and Malpighi attempted an ontogenetic approach, and studied ovules and developing and mature seeds. However, the resolving power of their microscopes was not sufficient to distinguish the boundaries between the nucellus and integuments. Their descriptions of the ovule and of seed coats are mainly stratigraphical, i.e., they emphasized the most conspicuous layers by differences in cell shape, cell wall thickness and consistency. This stratigraphical approach persisted till the first decade of the nineteenth century, and resulted in a profuse application of alternative terms, causing a terminological chaos (Bouman 1974, 1978a). Grew described a designedly formed, small foramen (micropyle) in the outer coat of young leguminous seeds. He compared this foramen with the bunghole of beer and wine barrels and assumed that it functions as a passage for “aiery particles to exite the fermentation”. During germination the foramen would, in this train of thought, promote the eruption of the radicle. After an analysis of the seeds of some 1,200 species, Turpin (1806) concluded that the “micropyle” is of universal occurrence and forms an essential part of all mono- and dicotyledonous seeds. He rejected Grew’s ideas and attributed to the micropyle a function associated with fertilization.