. Foundations of botany. Botany; Botany. THE EVOLUTIONARY HISTORY OF PLANTS 303 â¢â a development the macrospore produces an endosperm whicli is really a small cellular prothallium, concealed in the ovule. The microspore contains vestiges of a minute prothallium. In the angiosperms the macrospore and its prothallium are still less developed, and the microspore, or pollen grain, has lost all traces of a prothallium and is merely an antheridium which contains two generative ceUs.^ These are most easily seen in the pollen grain, but sometimes they are plainly visi- ble in the pollen tube (Fig. 16
. Foundations of botany. Botany; Botany. THE EVOLUTIONARY HISTORY OF PLANTS 303 â¢â a development the macrospore produces an endosperm whicli is really a small cellular prothallium, concealed in the ovule. The microspore contains vestiges of a minute prothallium. In the angiosperms the macrospore and its prothallium are still less developed, and the microspore, or pollen grain, has lost all traces of a prothallium and is merely an antheridium which contains two generative ceUs.^ These are most easily seen in the pollen grain, but sometimes they are plainly visi- ble in the pollen tube (Fig. 164). Phanerogams are distinguLshed from all other plants by their power of producing seeds, or enclosed macrosporangia, with embryos. 375. The Law of Biogenesis and the Relationships of the Great Groups of Plants.âOn summing up Sects. 872-374 it is evident that the sexual generation in general occupies a less and less important share in the life of the plant as one goes higher in the scale of plant life.^ In the case of the rockweed, for instance, the sexual generation is the plant. Among mosses and liverworts the sexual 1 Sometimes only one generative cell escapes from the pollen grain into the pollen tuhe, and there it divides into two cells. 2 A good many plants of low organization, however, are not known to pass through any sexual Fig. 217.âLongitudinal Section through Fertilized Ovule of a Spruce. ^fPolleu grains ; t, pollen tubes ; n, neck of the archegonlum ; a, body of archegonium with nucleus; e, embryo sac filled with 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 Bergen, Joseph Y. (Joseph Young), 1851-1917; Eastwood, Alice, 1859-1953. Boston, Ginn & Co.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbotany, bookyear1901
