. Morphology of gymnosperms. Gymnosperms; Plant morphology. 336 MORPHOLOGY OF GYMNOSPERMS cell divides into two distinct and unequal male cells, the cytoplasm of the body cell being divided unequally (fig. 386). The behavior of the tubes is interesting and suggestive. They may advance rapidly, reaching the female gametophyte at an early free nuclear stage (16-64 nuclei), or they may advance very slowly. The course may be very direct, resulting in a straight cleft through the tip of the nucellus, or it may be ex- tremely devious. In one case observed the tube ad- vanced directly half-way throug
. Morphology of gymnosperms. Gymnosperms; Plant morphology. 336 MORPHOLOGY OF GYMNOSPERMS cell divides into two distinct and unequal male cells, the cytoplasm of the body cell being divided unequally (fig. 386). The behavior of the tubes is interesting and suggestive. They may advance rapidly, reaching the female gametophyte at an early free nuclear stage (16-64 nuclei), or they may advance very slowly. The course may be very direct, resulting in a straight cleft through the tip of the nucellus, or it may be ex- tremely devious. In one case observed the tube ad- vanced directly half-way through the tip of the nucellus; then proceeded spirally downward and out- ward to the peripheral cells of the nucellus, several of which it destroyed; then turned abruptly inward, penetrated the nucellus at the level of the arche- •gonium, crossed the top of the endosperm, and dis- charged into the arche- gonium on the opposite side. In another case a wandering tube penetrated the inner integument before turning back into the nu- cellus. Very frequently the tube pushes into the embryo sac at the free nuclear stage, making a deep invagination (often to the middle of the sac), and from this pocket it turns back. Figs. 384, 385.—Torreya taxifolia: fig. 384, tip of nucellus with pollen chamber (disintegrated tip of nucellus) containing a two-celled micro- spore, the smaller cell being the generative cell and the larger the tube cell; pc, pollen chamber; X220; fig. 38s, end of pollen tube in contact with embryo sac, which is in free nuclear stage; in the tube the stalk and tube nuclei are in advance of the body cell; X460.—After Coulter and Land (ioi).. 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
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