GAMETOGENESIS AND SPOROGENESIS 



207 



separating the projecting egg haustoriiim eventually ruptures, the 

 cytoplasm of the egg and nutritive cells then becoming continuous. In 

 the cycads the egg cytoplasm appears relatively free from conspicuous 

 nutritive inclusions, but in conifers, such as Pinus and Agathis, there 

 are often large masses of stainable ergastic material and other substances 

 of uncertain origin and composition. The nucleus of the gymnosperm 

 egg resembles that of certain animal eggs in containing an unusually large 

 amount of material not incorporated in the chromosomes at the time of 

 mitosis. 



D U- . . ^v' . ^Islisjife^j^G^ 





B 



Fig. 124. — Stages in spermatogenesis in Dioon edule. A, "body-cell" with black 

 granules in cytoplasm. B, two blepharoplasts differentiated. C, body-cell with two 

 blepharoplasts; prothallial and stalk cells below; all in end of pollen tube. D, fragmenta- 

 tion of blepharoplast in spermatid as spiral band begins to form. E, portion of edge of 

 section of spermatozoid (cf. Fig. 116, D) showing spiral blepharoplast cut at two points and 

 cilia growing from it. {After Chamberlain, 1909.) 



In the gymnosperms there are two principal types of spermatogenesis, 

 some of the orders (Cycadales, Ginkgoales) having ciliated spermato- 

 zoids^- and the others (Coniferales, Gnetales) non-motile male cells. 

 In most cycads and Ginkgo a greatly enlarged "body-cell" in the devel- 

 oping pollen tube gives rise to two spermatozoids. In Dioon, for example 

 (Fig. 124), numerous "black granules'' appear in the body-cell cytoplasm. 

 Two blepharoplasts now develop, apparently by the enlargement of two 

 of the black granules, and take up positions on opposite sides of the 

 nucleus. Very conspicuous radiations^^ appear about them as the 

 body-cell divides. The mitotic figure is wholly intranuclear, and, 

 although the blepharoplasts remain opposite its poles, they appear to 

 have no direct connections with it. A wall appears between the two 

 daughter nuclei at the close of mitosis; in each of the resulting cells a 



12 Hirase (1894), Ikeno (1898), Fujii (1898, 1899), Webber (1897, 1901), Caldwell 

 (1907), Miyake (1906), Chamberlain (1909, 1916), Kuwada and Maeda (1929). 



13 Hirase (1894), Fujii (1899), and Kuwada and Maeda (1929) report that these 

 are invisible in living cells. 



