. Morphology of spermatophytes. [Part I. Gymnosperms]. Gymnosperms; Plant morphology. 46 MORPHOLOGY OP SPERMATOPHYTES. At the end of July the body cell increases still more in size, becoming rich in contents, and its nucleus becoming very large. At this stage the blepharoplasts appear, and finally assimie their polar positions at the extremities of the long axis of the ellip- soidal nucleus. This stage persists for three weeks—that is, until the third week before fertilization. At the beginning of August the tube nucleus begins to pass back to the grain end of the tube, which it reaches in abo
. Morphology of spermatophytes. [Part I. Gymnosperms]. Gymnosperms; Plant morphology. 46 MORPHOLOGY OP SPERMATOPHYTES. At the end of July the body cell increases still more in size, becoming rich in contents, and its nucleus becoming very large. At this stage the blepharoplasts appear, and finally assimie their polar positions at the extremities of the long axis of the ellip- soidal nucleus. This stage persists for three weeks—that is, until the third week before fertilization. At the beginning of August the tube nucleus begins to pass back to the grain end of the tube, which it reaches in about two weeks, consorting with the body cell, or with the male cells, until fertilization. During this retreat of the tube nucleus and abandonment of the absorbing tube system, the endosperm be- gins to develop a beak between the two archegonia. Hirase sug- gests that its significance is to be explained by the fact that the tissue between the nucellar beak and the embryo sac has been broken down by the •deepening of the pollen cham- ber and by the absorptive work of the pollen-tube system, and that the heavy beak settles down upon the sac. In about two weeks the endosperm beak looks like a small column, with its summit against the nucellar beak, " like a tent supported by its center pole," in the shelter of which there is freedom for the final processes connected with fertilization. Pressure upon the grain ends of the pollen tubes which happen to lie under " the tent" is thus avoided, and these ends become very turgid and are directed toward the near-lying archegonia (Fig. 33). During the third week before fertilization—that is, about the last of August—the body cell begin^ division, and the cili- ated male cells are organized. The swollen tip of the pollen, tube, capped by the old wall of the pollen grain, now contains in a group the two male cells, the tube nucleus, and the vege- tative cell, together with whatever may remain of the stalk cell. At t
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