. Botany for high schools and colleges. Botany. CELL FORMATION BY DIVISION. 41 about certain points without tlie previous formation of nu- clei [d, e). In either case firm walls are secreted about the spores while yet in the mother-cell and surrounded by the unused part of its protoplasm. 55.—The most striking example of this variety of internal cell-formation is to be found in the development of the endosperm cells in the embryo sac of Phanerogams. The protoplasm which occupies the cavity of the embryo sac pre- sents here and there points of condensation or concentration, which in a little ti
. Botany for high schools and colleges. Botany. CELL FORMATION BY DIVISION. 41 about certain points without tlie previous formation of nu- clei [d, e). In either case firm walls are secreted about the spores while yet in the mother-cell and surrounded by the unused part of its protoplasm. 55.—The most striking example of this variety of internal cell-formation is to be found in the development of the endosperm cells in the embryo sac of Phanerogams. The protoplasm which occupies the cavity of the embryo sac pre- sents here and there points of condensation or concentration, which in a little time become as many nuclei (Fig. 33, A^ n, n), each containing a nucleolus. These nuclei are the first in- dications of the form- ing cells. Protoplasm gathers about the nu- clei and forms globu- lar or ovoid masses (A, a, a), which, after acquiring a certain size, secrete a thin wall of cellulose on their surfaces (A,c, c', cl). By the continued production of new cells within the em- bryo sac, in this way, they finally become crowded together into a loose tissue, in whose intercellular spaces portions of the unconsumed protoplasm yet remain (B). After their forma- tion the cells go on increasing in numbers by simple fission (a) Saclis f makes a strong distinction between the cases of internal cell-formation where, on the one hand, a 2y(^rt only, and, on the other, * The student is here referred to the account of the formation of endosperm cells in Duchartre's "Elenienis de Botanique," pp. 37-39 ; and also to Hofmeister's " Lelire von der Pfianzenzelle," Section 17. f " Lehrbuch," 4te auf. In the English translation of the third edi- tion all cases of fission are included under the Formation of Cells by Division of the Fig. 31.—Development of the ppores of Aspidium filix-mas. /, the spore-mother-ccll, with nucleus ; //, the nucleus absorbed ; ///. two nuclei, and the division of the protoplasm into two portions; IV, four nuclei; F.
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