. Morphology of gymnosperms. Gymnosperms; Plant morphology. CONIFERALES (PINACEAE) 275. and the pollen, caught in this pollination drop, is conveyed to the nucellus (fig. 315). The pollen tube begins to grow into the nucellus as soon as the spore is deposited, and continues to develop until it is checked by cold weather. The next spring the tube begins to renew its penetration of the nucellus during April, about a year after the pollen mother cell entered upon the reduction divisions, the large tube nucleus enters the tube, and at the same time the generative cell divides into the stalk cell (
. Morphology of gymnosperms. Gymnosperms; Plant morphology. CONIFERALES (PINACEAE) 275. and the pollen, caught in this pollination drop, is conveyed to the nucellus (fig. 315). The pollen tube begins to grow into the nucellus as soon as the spore is deposited, and continues to develop until it is checked by cold weather. The next spring the tube begins to renew its penetration of the nucellus during April, about a year after the pollen mother cell entered upon the reduction divisions, the large tube nucleus enters the tube, and at the same time the generative cell divides into the stalk cell (toward the vegetative cells) and the body cell (toward the free cavity of the spore) (fig. 313). The stalk cell is sterile (persistently so among gymnosperms), and may represent the stalk cell of an antheridium, while the body cell may be the true primary spermatogenous cell. The pollen tube branches as it traverses the nucellus, not so extensively as do the tubes of cycads and of Ginkgo, but sufficiently to indicate its primi- tive haustorial function. After its second start, the pollen tube consumes about two months in traversing the nucellus, reaching the archegonium about the first of July. The body cell rounds off, and becoming freed from the stalk cell passes into the tube. The separation of the body cell from the stalk cell frees the nucleus of the latter, and it also passes into the tube, where the nucleus of the body cell divides, forming two nuclei which do not become separated by a wall. The body cell, with its two nuclei, then passes down the tube, and when it has reached the tip, the four nuclei may be found grouped together, usually with the stalk and tube nuclei in advance. At this stage the contour of the body cell may be quite distinct (fig. 316), or rather indefinite (fig. 317), or its cytoplasm may have become so mingled with that of the pollen tube that the nuclei lie in a common mass of cytoplasm (fig. 318). The division of the body cell occurs just before
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