. Morphology of gymnosperms. Gymnosperms; Plant morphology. CYCADALES 139 I S3 to the endosperm, contains a substance related to pectin, toward the middle the pectin is replaced by cellulose, and the cellulose is replaced in turn by suberin in the outer part of the endospore, where it borders upon the suberized exo- spore. In structure the endospore is rather homogeneous, while the exospore is formed of little columns or fibrillae, which give it a dis- tinctly striated appearance (fig. 152). The outer walls of the endosperm cells bordering upon the endospore become suberized, and might some- t

. Morphology of gymnosperms. Gymnosperms; Plant morphology. CYCADALES 139 I S3 to the endosperm, contains a substance related to pectin, toward the middle the pectin is replaced by cellulose, and the cellulose is replaced in turn by suberin in the outer part of the endospore, where it borders upon the suberized exo- spore. In structure the endospore is rather homogeneous, while the exospore is formed of little columns or fibrillae, which give it a dis- tinctly striated appearance (fig. 152). The outer walls of the endosperm cells bordering upon the endospore become suberized, and might some- t

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. Morphology of gymnosperms. Gymnosperms; Plant morphology. CYCADALES 139 I S3 to the endosperm, contains a substance related to pectin, toward the middle the pectin is replaced by cellulose, and the cellulose is replaced in turn by suberin in the outer part of the endospore, where it borders upon the suberized exo- spore. In structure the endospore is rather homogeneous, while the exospore is formed of little columns or fibrillae, which give it a dis- tinctly striated appearance (fig. 152). The outer walls of the endosperm cells bordering upon the endospore become suberized, and might some- times be mistaken for a part of the endospore itself. The mem- brane in Dioon edule is shown in figs. 136,137, where it is in contact with the endosperm above the arche- gonia; and in fig. 153, which shows the comparatively homogeneous endospore and the exospore con- sisting of club-shaped bodies with an ovoidal outer portion connected with the endospore by a stalk. In sections more than i or 2 /^ in thickness, the region of the stalks appears as a nearly black line, so that there seem to be three layers, the extra layer being only an optical effect due to the stalk region,. Figs. 152,153.—Themegaspore membrane of the cycads: fig. 152, Cycas revoluta; three free nuclei of the endosperm at the left, cells of the endosperm jacket at the right, and the megaspore membrane (4.5 /* thick) between them; fig. 153, Dioon edule; section of megaspore mem- brane showing inner homogeneous layer and outer layer of club-shaped bodies; X 1,200.—Fig. 152, after Thomson (45); fig. 153, after Chamberlain (46). THE MALE GAMETOPHYTE The microspore is the first cell of the male gametophyte. The peculiar thickening of the wall of the microspore mother cell, making it resemble a heavy, foiur-celled case containing the four spores, has been described by Jueanyi (5) for Ceratozamia longifolia, and by Teexje (ii) for Zamia muricata (fig. 154). Jusanyi (5) gave also a fairly full account of the germina