. Carnegie Institution of Washington publication. GYMNOSPERMS. '59 During the final stages in the development of the spermatozoid the proximal end of the pollen tube, which is still capped by the exine of the spore, grows downward into the prothallial cavity as in Zamia (Fig. 65, A). This cavity in Cycas, according to Ikeno, is filled with a watery fluid derived largely from the archegonia, and in which the spermatozoids swim on escaping from the pollen tube. Webber is of the opinion that in Zamia this fluid is derived largely from the pollen tube. The spermatozoids in Cycas, on escaping from
. Carnegie Institution of Washington publication. GYMNOSPERMS. '59 During the final stages in the development of the spermatozoid the proximal end of the pollen tube, which is still capped by the exine of the spore, grows downward into the prothallial cavity as in Zamia (Fig. 65, A). This cavity in Cycas, according to Ikeno, is filled with a watery fluid derived largely from the archegonia, and in which the spermatozoids swim on escaping from the pollen tube. Webber is of the opinion that in Zamia this fluid is derived largely from the pollen tube. The spermatozoids in Cycas, on escaping from the pollen tube, swim about rapidly, and in a short time penetrate the egg. That part of the egg at which a spermatozoid enters is de- pressed, giving the impres- sion that it came against the egg with some force. The nucleus of the spermatozoid now escapes from its cyto- plasmic mantle and migrates toward the nucleus of the egg. The cytoplasm and blepharoplast are left in the upper part of the egg as in Zamia (Fig. 66, A, B), where they undergo disor- ganization It freaueiltlv FIG. 66.—Fecundation of egg-cells in Za»«a.—(After 3 Webber.) happens that several sperm- „ . .. , . , , A, egg-cell immediately alter coming together of male and atOZoids reach the egg, but, female nuclei; the ciliferous band of fecundating sper- as a rule, only one penetrates ma'oz°id lies in upper end of eg^ asecond sp'rmat°- J zoid trying to gain entrance is shown at apex of egg. into its interior, the Others B, similar to A, but showing longitudinal section of ciliferous remaining at the surface. band inupper end ofegg' Whether more than one male nucleus ever fuses with the egg-nucleus is not known. When male and female nuclei come in contact they are readily distinguished from each other, the male being smaller, with a more finely granular threadwork. Both are in the resting stage. The male nucleus seems to press against the female, forming a depression in the latter. In a short time the
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