. Elementary botany . ^AreH Fig. 272. Last division of the egg in the white pine cutting off the ventral canal cell at the apex of the archegonium. End, endosperm; Arch, archegonium. theridium. there being no wall formed. The sperm mother cell also passes down the tubular sac, and divides again into two sperm cells, as shown in fig. 270. About this time, or rather a little earlier, with the pollen tube part way through the nucellar cap, winter overtakes it, and all growth ceases until the following spring. 426. Fertilization.—In the spring the advance of the pollen tube con- tinues, and it fin
. Elementary botany . ^AreH Fig. 272. Last division of the egg in the white pine cutting off the ventral canal cell at the apex of the archegonium. End, endosperm; Arch, archegonium. theridium. there being no wall formed. The sperm mother cell also passes down the tubular sac, and divides again into two sperm cells, as shown in fig. 270. About this time, or rather a little earlier, with the pollen tube part way through the nucellar cap, winter overtakes it, and all growth ceases until the following spring. 426. Fertilization.—In the spring the advance of the pollen tube con- tinues, and it finally passes through the nucellar cap about the time that the archegonia are formed and the egg cell is mature, as shown in fig. 271. The pollen tube now opens and the sperm cells escape into the archegonium, and later one of them fuses with the Qgg nucleus. The fertilized egg is now ready to develop into the embryo pine. 427. Homology of the parts of the female cone.—Opinions are divided as to the homology of the parts of the female cone of the pine. Some consider entire cone to be homologous with a flower of the angiosperms. The en-
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Keywords: ., bookcentury1800, bookdecade1890, bookpublisher, booksubjectbotany
