Author Description

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1896 Excerpt:...the other the nucleus of the egg, which extends below the two synergidae (figs. 50--52). All these cells are bounded by a clearly defined protoplasmic membrane, and the protoplasm within shows a somewhat vacuolate structure, especially in the egg. Here, too, the demonstration of the centrosphere was not satisfactory, but it may have been on account of defective methods. The cells covering the apex of the embryo-sac divide but little, but are not encroached upon by its growth; while the lateral cells of the nucellus are much compressed and the inner layers completely destroyed, so that at the time of fertilization there is but a single complete layer of cells bounding the sides of the embryo-sac (fig. 57). In the course of these investigations a number of striking departures from the normal type of embryo-sac were observed. In the one shown in fig. 54 there was apparently no absorption of the cells above the embryo-sac, and in the embryo-sac itself the usual course of development had not gone on in a normal way. There were three 'nuclei, one somewhat larger than the others, at the apex of the sac, and it looked as if there might be an imperfect septation by very thin walls; but the latter may have been simply sections of the walls of the nucellar cells surrounding the embryo-sac. The egg apparatus was not differentiated, but the polar nuclei were formed as usual. The antipodal cells were, however, six instead of three (fig. 55), presumably due to an extra division in each, subsequent to the formation of the polar nuclei. Another striking instance is shown in fig. 56. Here, apparently, fertilization had not been effected and the embryo-sac had become filled with parenchymatous tissue, composed of elongated, somewhat thick-walled cells. As this was the only in...