GROWTH OF THE EMBRYO OF GINKGO BILOBA UNDER EXPERIMENTAL CONDITIONS. I. ORIGIN OF THE FIRST ROOT OF THE SEEDLING IN VITRO

Abstract

THE MORPHOLOGY AND PHYSIOLOGY of the growth in vitro of the embryo into a seedling have not beeni thoroughly investigated. The observations of La Rue (1936) and of La Rue and Avery (1938) that small, immature embryos grown in vitro did not pass through -the successive stages of normal embryology but grew immediately into a seedling appear to be applicable to a wide variety of plants. As La Rue (1936) pointed out, such experiments constitute a beginning in the study of experimental embryology. If one uses an embryo of sufficient size and in which there are no difficulties in achieving growth, it should be possible to introduce a variety of chemical and physical changes into the experimental procedures and thus gain valuable information on their effects. Three regions of the embryo of a vascular plant may be profitably experimented uponi in such culture studies. The cotyledons usually function as haustorial structures before and/or after germination of an embryo. La Rue (1936) showed that cotyledons of in vitro cultured embryos do not develop either qualitatively or quantitatively as they do in seed-grown embryos. The tip of the hypocotyl is the site of origin of the apex of the primary root. The other end of the axis of the embryo is the shoot apex. The latter meristem usually begins the formation of leaf primordia and subjacent stem tissues while the embryo is in the seed and continues these growth processes when the embryo germinates into the seedling. One of the most important subjects in an experimental study of the growth of embryos is the effect of these opposed apical meristems on the development of the seedling axis. Before utilizing in vitro procedures for growing the embryos of Ginkgo after experimental treatment, it was necessary to determine whether the embryo could be grown into an approximately normal seedling. Emphasis was placed upon the origin and structure of the first root produced by the embryo under these experimental conditions. It was necessary to know whether the structure of the root was normal when grown in vitro. The bases for comparison were the -critical studies of Lyon (1904) and of Sprecher (1907). MATERIALS AND METHODS.The partially matured embryos in seeds of Ginkgo have been found to be well suited as material for these experiments.