. Morphology of gymnosperms. Gymnosperms; Plant morphology. 393 MORPHOLOGY OF GYMNOSPERMS merges insensibly into the root cap. There are thus three stages of suspensor-formation: the first elongation in connection with the nucleus which later becomes the nucleus of the embryo cell; the second and chief elongation in connection with the smaller nucleus of the proembryonal cell; and the formation of a secondary, multicellular suspensor by the basal cells of the emjbryo. Although several embryos may begin to develop in a single ovule, only one of them reaches maturity. In Ephedra trifurca the occ
. Morphology of gymnosperms. Gymnosperms; Plant morphology. 393 MORPHOLOGY OF GYMNOSPERMS merges insensibly into the root cap. There are thus three stages of suspensor-formation: the first elongation in connection with the nucleus which later becomes the nucleus of the embryo cell; the second and chief elongation in connection with the smaller nucleus of the proembryonal cell; and the formation of a secondary, multicellular suspensor by the basal cells of the emjbryo. Although several embryos may begin to develop in a single ovule, only one of them reaches maturity. In Ephedra trifurca the occurrence of vivipary is evident, at least in some cases, numerous seedlings being observed to have emerged from the seeds while the strobili were still attached to the stem. In any event, the period of rest for the embryo must be very short, and favorable conditions for growth may eliminate it entirely. The whole period from the first appearance of the ovulate strobili to the "germination" of the seed is approximately six months. In Welwitschia the fertilized egg, within the prothallial tube, behaves as does the pro- embryonal cell of Ephedra. As described by Pearson (27), it elongates toward the top of the endosperm, and the first nuclear division is followed by a cleavage wall which cuts off a terminal embryo cell. The general statement has been that in Wel- witschia and Gnetum there is no free nuclear division in the first stages of embryo-forma- tion, but that the first division of the fusion nucleus is accompanied by waU-formation, as in the angiosperms. This statement must be revised, for in Welwitschia the fusion nucleus produces two free nuclei, which are later separated by a wall that holds no relation to the spindle of the fusion nucleus. The suspensor cell of Welwitschia elongates extremely, becoming much coiled and persistent, and the embryo cell produces a pyramidal group of cells (about. Fig. 4S4.—Welwitschia mirabilis: a young embryo consisting of a py
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