THE ANATOMY OF THE EMBRYO OFCEDRUSIN THE DORMANT STAGE

Abstract

There are some very interesting anatomical features which beconme differentiated in the embryos of matured conifer seeds. Some differences may be found between the embryos of different genera and families, even though the plan of meristematic organization in the embryo is remarkably uniform throughout the Coniferales. A survey of the literature shows that relatively little which has to do with details in cellular arrangement and organization has been recorded. Most of the investigations have been concerned with the gross external morphologv including size, shape, and number of cotyledons. Schleiden (I3), in his text-book, was among the first who gave a description of tlhe half-grown embryo of a pine and of the embryo in the stage of the matured seed. He reported the order of appearance of the primordia for the organs: root tip, stem tip, and cotyledons. Strasburger (14), the largest single contributor on this subject, corrected Schleiden's error concerning one feature, namely, that it is the plerome apex of the root and not the true root tip which is the first part of the embryo to become differentiated. Schacht (I2) described the meristem of the root tip in a pine and Strasburger gave us more fully the meristematic organization of the root tip and stem tip of various conifers. 1Ie also gave a description of the more mature embryos of Thuja occidentalis, Pinus pnitvilio, Picca vulgaris, Tarus baccata and Ephedra altissima, pointing out the great uniformity in the anatomical structure and organization of the embryo in conifers. His investigations did not include Cedrus which has, at least externally, some striking differences from most of the remaining genera of Abietineae. A few other stages of conifer embryos have occasionally been described such as the descriptions of germinating seedlings by Lord Avebury (ii). In taxonomic monographs and general text-books there are scattered records concerning the size, shape and the number of cotyledons, and occasionally these show sections of seeds or the embryos removed from the seeds. In an extensive series of studies of the vascular anatomy of conifer seedlings, Hill and De Fraine (7) have given a conmprehensive comparison of the seedlings in stages after the early vascular elements are well organized. From these we know the facts concerning the number of cotyledons in a large series of species, with records of the vascular connections in the root and transition region, occurrence and prevalence of fused cotyledons and cotyledonary tubes, divided or fused vascular strands, etc.