Quarterly Journal of Microscopical Science (Volume 13)

Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: four cells a peripheral division now takes place, not simultaneously, but in rapid succession, the young embryo consisting of four central quadrant cells, and four outer Dermatogen cells (fig. 3). The first division of the embryo mother-cell indicated the position of the cotyledons, while the transverse division indicates the separation between the upper stem or cotyledonary part of the embryo from the lower or hypocoty- ledonary portion. The outer cells are the mother-cells of the Dermatogen, and the epidermis and its structures are at once and for ever thus separated from the inner tissues. The Dermatogen cells begin to multiply before the inner cells (fig. 4). In the hypocotyledonary portion the inner cells first divide longitudinally, and then division in the cotyledonary portion takes place. In the hypocotyledonary part the outer cells of the inner portion develope the Periblem mother-cells, the inner the Plerom (fig. 5). During these divisions in the embryo mother-cell the cells of the suspensor have also been increasing, the number, however, varying and not being definite. The penultimate cell of the proembryo, i.e. that next the embryo mother-cell, plays an important part in the development. This cell becomes more convex, and soon forms a portion of the embryo, appearing as if it were an integral part of it. This cell divides into two, the upper forming part of the interior of the young embryo, the other closing it below. This forms what Hanstein calls the hypophyse. The hypophyse cells sooner or later develope further; division also taking place in the interior cells, while from the outer cell (formed by division) of the Plerom the procambium cells develope at a later period (fig. 6). At this stage it will be observed that the Periblem and Plerom cells are bo...