. Botany for high schools and colleges. Botany. G YMNOSPEBMM. 403 jogue of a macrospore, whicli liere is not freed from tlie parent plant. The endosperm clearly bears the same rela- tion to the embryo sac as the prothallium of Isoetes does to the macrospore ; and the corpuscula are slightly modified archegonia. In some corpuscula the resemblance to arche- gonia is very marked, the germ-cell below being surmounted by a short neck ; Strasburger has even discovered a rudi- mentary axial-cell, thus completing the correspondence of these organs to those of the higher Pteridophytes. 512.—Fertilizati
. Botany for high schools and colleges. Botany. G YMNOSPEBMM. 403 jogue of a macrospore, whicli liere is not freed from tlie parent plant. The endosperm clearly bears the same rela- tion to the embryo sac as the prothallium of Isoetes does to the macrospore ; and the corpuscula are slightly modified archegonia. In some corpuscula the resemblance to arche- gonia is very marked, the germ-cell below being surmounted by a short neck ; Strasburger has even discovered a rudi- mentary axial-cell, thus completing the correspondence of these organs to those of the higher Pteridophytes. 512.—Fertilization is effect- ed by means of the pollen, which comes in contact with the apex of the ovule. It is transported from the male flowers mostly by the wind, which accounts for the im- mense quantity p r o d u c e d. When the ovule has reached the proper stage the micropyle is filled with a fluid, which, dry- ing, carries the adherertt pollen grains into contact with the apex of the ovule body, where they germinate and form pol- len tubes ; the latter penetrate the soft tissue of the ovule and eventually reach the corpus- cula (Fig. 299). In those cases where the corpuscula are separated from one another each pollen tube comes in con- tact with only one corpusculum (Figs. 297, B, and 299) ; but when the corpuscula are close together a single pollen tube may come in contact with all of them (Fig. 298, 1 and 2). The union of the protoplasm of the pollen tube with that of the germ-cell appears to take place by diffusion through the wall of the former, as no openings in it have been discovered. After fertilization the protoplasm in the germ-cell becomes more turbid and granular, and soon at the base a transverse partition is formed, cutting off a cell, which is the rudiment. Fig. 299.—Diagrammatic section of an ovnle of Piniis, showing fertiliza- tion, i, integument or coat of tlie ovuie; OT, the micropyle ; k, the body or " nucleus" of the ovule ; e, the em- bryo sac, fill
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