General physiological problems of embryogenesis in plants

Abstract

The ontogenetic development of the sporophyte of a vascular plant properly begins with the fertilized ovum; for in it is the complement of genes which, in conjunction with extrinsic factors, will determine the distinctive, specific, morphological development of the young embryo and of the enlarging sporophyte. It may be that botanists have tended to take the zygote for granted — as it were as something given — and to proceed with observations on its polarity, growth, segmentation and differentiation as the ontogenetic development proceeds. But if one reflects on the facts, scanty though they may be in some respects, it becomes apparent that the ovum both before and after fertilization must be a complex, organized micro-structure, and that not only the early stages of embryo-genesis, but many of the major phenomena of ontogenesis, are referable to the organization of the ovum and zygote. Unfortunately, little is known about this phenomenon in plants — the zoologists have made much greater progress in this matter — but that it has real existence may be inferred from such observations as the very early establishment of polarity in the embryo. Illustrations do occur in the morphological literature of plant embryogenesis which indicate the existence of differences in protoplasmic structure at the apical and basal poles of the ovum or zygote, but these are rather exceptional. Factors which may determine this organization are discussed later in this article.