. Elementary botany. Botany. FURTHER STUDIES ON GYMNOSPERMS. 2\J group, that the sperm cells are well-formed spermatozoids. In zamia each one is shaped somewhat like the half of a biconvex lens, and around the con- vex surface are several coils of cilia. Alter the pollen tube has grown down through the nucellus, and has reached a depression at the end of the prothallium (endosperm) where the archegonia are formed, the spermatozoids are set free from the pollen tube, swim around in a liquid in this depression, and later fuse with the egg. In gingko and cycas these spermatozoids were first disco
. Elementary botany. Botany. FURTHER STUDIES ON GYMNOSPERMS. 2\J group, that the sperm cells are well-formed spermatozoids. In zamia each one is shaped somewhat like the half of a biconvex lens, and around the con- vex surface are several coils of cilia. Alter the pollen tube has grown down through the nucellus, and has reached a depression at the end of the prothallium (endosperm) where the archegonia are formed, the spermatozoids are set free from the pollen tube, swim around in a liquid in this depression, and later fuse with the egg. In gingko and cycas these spermatozoids were first discovered by Ikeno and Hirase in Japan, and later in zamia by Webber in this country. In figs. 283-286 the details of the male prothallia and of fertilization are shown. 435. The sporophyte in the gymnosperms.— In the pollen grains of the gymnosperms we easily recognize the characters belonging to the spores in the ferns and their allies, as well as in the liverworts and mosses. Thev belong to the. Fig. 284. Fertilization in cycas, small spermatozoid fusing with the same series of organs, are borne on the same larger female nucleus of the egg. , • r i i i • The eSS protoplasm fills the phase or generation of the plant, and are practi- archegonium. (From drawings "y formed in the same general way, the by Hirase and Ikeno) cally formed in the same general way, variations between the different groups not being greater than those within a single group. the Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Atkinson, George Francis, 1854-1918. New York, H. Holt and company
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