. An introduction to vegetable physiology. Plant physiology. 446 VEGETABLE PHYSIOLOGY megasporangium; in the Gymnosperms it falls upon the megasporangium itself; in the Angiosperms upon the stigma of the pistil in which the megasporangia are hidden. When it germinates the prothallium or gametophyte takes the form of a long tube, which bores its way through the intervening tissues till it reaches the megaspore itself, close to the archegonium in the first case, and to the oosphere in the Angiosperms, where there is no archegonium. In the Gymnosperms the tube, the so-called pollen-tube, con- tai
. An introduction to vegetable physiology. Plant physiology. 446 VEGETABLE PHYSIOLOGY megasporangium; in the Gymnosperms it falls upon the megasporangium itself; in the Angiosperms upon the stigma of the pistil in which the megasporangia are hidden. When it germinates the prothallium or gametophyte takes the form of a long tube, which bores its way through the intervening tissues till it reaches the megaspore itself, close to the archegonium in the first case, and to the oosphere in the Angiosperms, where there is no archegonium. In the Gymnosperms the tube, the so-called pollen-tube, con- tains a single antheridium, which produces two Fig. 182.—Development of the Aeohegohium or the Fern. (After Kny.) 1, 2, 4, 5, 7, 8, 9 Successive stages; 3) 6 transverse sections of the neck region of 4 and 6. These are generally undifferentiated portions of protoplasm, but in Ginkgo, Zamia, and in some species of Cycas they have been found to be ciliated antherozoids. In the Angiosperms there is no antheridium, but two gametes which show no differentiation are produced in the pollen-tube. From the great preponderance of the nuclear matter they contain they are often spoken of as the generative nuclei. Fusion of the latter, or of the antherozoid, with the oosphere, becomes possible by a deliquescence of the sepa- rating walls, and in all cases a single male gamete fuses with an oosphere. Where several oospheres are found upon the same prothallium, as in the Gymnosperms, more. 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 Green, J. Reynolds (Joseph Reynolds), 1848-1914. London, J. & A. Churchill
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