. Morphology of gymnosperms. Gymnosperms; Plant morphology. GINKGO ALES 207 becoming brown and forming a resistant beak that long persists as a cap on the sac. The pollen grains, carried well below the beak by the deepening of the chamber, send out their tubes in every direction into the adjacent nucellar tissue, but chiefly away from the embryo. 240 239 Figs. 235-240.—Ginkgo biloba: the male gametophyte; fig. 235, pollen grain, showing evanescent prothallial ceU and persistent prothallial cell; the mitosis in the antheridium initial will form the generative and tube cells; April 24; X500; fig
. Morphology of gymnosperms. Gymnosperms; Plant morphology. GINKGO ALES 207 becoming brown and forming a resistant beak that long persists as a cap on the sac. The pollen grains, carried well below the beak by the deepening of the chamber, send out their tubes in every direction into the adjacent nucellar tissue, but chiefly away from the embryo. 240 239 Figs. 235-240.—Ginkgo biloba: the male gametophyte; fig. 235, pollen grain, showing evanescent prothallial ceU and persistent prothallial cell; the mitosis in the antheridium initial will form the generative and tube cells; April 24; X500; fig. 236, poUen at the shedding stage, with prothallial, generative, and tube cells; X500; fig. 237, part of poUen tube July 10; X500; fig. 238, the nucleus of the generative cell has divided, the stalk and body nuclei lying side by side; July 11; Xsoo; fig. 239, the body cell has divided; blepharoplasts are faintly visible; X120; fig. 240, the two sperms produced by the body cell; September 11; X226.—After Hirase (16). sac, and often directly toward the beak. Into these young tubes the tube nuclei pass, and remain there so long as the tube system is developing. About the beginning of July, the tubes have penetrated the nucel- lar tissue deeply and have branched freely, the tube nucleus remaining where a tube begins to branch. This extensive system of branching. 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
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