. Morphology of gymnosperms. Gymnosperms; Plant morphology. 392 MORPHOLOGY OF GYMNOSPERMS. Fig. 444.—Ephedra trifurca: fer- tUization; pt, pollen tube; v, ventral nucleus; »Si, 0, fusing nuclei; Wa^second male nucleus; X21S.—After Land (23). functioning male nucleus slips out of its cytoplasmic sheath in the periphery of the egg, and probably this is true of the species of Ephedra in general. In Welwitschia the pollen tubes and prothallial tubes come in contact in the nucellar cap. How the transfer of male cells or nuclei is effected has not been observed, but several eggs are fertilized in ea
. Morphology of gymnosperms. Gymnosperms; Plant morphology. 392 MORPHOLOGY OF GYMNOSPERMS. Fig. 444.—Ephedra trifurca: fer- tUization; pt, pollen tube; v, ventral nucleus; »Si, 0, fusing nuclei; Wa^second male nucleus; X21S.—After Land (23). functioning male nucleus slips out of its cytoplasmic sheath in the periphery of the egg, and probably this is true of the species of Ephedra in general. In Welwitschia the pollen tubes and prothallial tubes come in contact in the nucellar cap. How the transfer of male cells or nuclei is effected has not been observed, but several eggs are fertilized in each ovule, and Pearson says (26) that the cyto- plasm of the fusion nucleus is mainly that of the male cell, which would practically repeat the behavior observed in the sexual fusion of the Taxaceae and Taxodium. In Gnetum (15) one or more pollen tubes enter the embryo sac, and their tips are observed among the free nuclei (fig. 419, /). The tip of the tube becomes distended and discharges its con- tents (usually four nuclei), both male cells being free in the sac and functioning. Approximately as many eggs are fertilized as there are male cells discharged into the' sac, that is, twice as many as there are entering pollen tubes. About the fusion nucleus a dense layer of cytoplasm appears and soon a cell mem- brane is formed. The discharge of male cells into an embryo sac. 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 Coulter, John Merle, 1851-1928; Chamberlain, Charles Joseph, b. 1863; Coulter, John Merle, 1851-1928. Morphology of spermatophytes. Part I. Gymnosperms. Chicago, University of Chicago Press
Size: 905px × 2760px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublisherchicagouniversityo
