. Text-book of botany, morphological and physiological. Botany. FILICINE&. 46g among the Dichotomese in that they possess spores of two kinds, the microspores and the microspores. As in the Rhizocarpeae so here the carrying back of sexual differentiation to the development of the spores is associated with this peculiarity, that the spores in gepminating seem to attain their object, the formation of re- productive organs, as directly as possible, for the prothallium is not a plant capable of independent growth but a development of tissue within the spore. The mode in which this is brought a
. Text-book of botany, morphological and physiological. Botany. FILICINE&. 46g among the Dichotomese in that they possess spores of two kinds, the microspores and the microspores. As in the Rhizocarpeae so here the carrying back of sexual differentiation to the development of the spores is associated with this peculiarity, that the spores in gepminating seem to attain their object, the formation of re- productive organs, as directly as possible, for the prothallium is not a plant capable of independent growth but a development of tissue within the spore. The mode in which this is brought about in the Ligulatse differs in essential points from that obtaining among the Rhizocarpeae. The Microspores of Isoetes and Selaginella do not produce the mother-cells of the antherozoids immediately from their contents, as was formerly thought. To the treatise of Millardet mentioned in the foot-note we owe our knowledge of the fact, so important in connection with the relationship of the higher Cryptogams to the Gymnosperms, that at the period when the microspores are ripe, their contents are transformed into a mass of tissue consisting of but few cells. One of these cells. FIG. 329.—Germination of the microspores of Isoetes lacustris (after Millardet). A and C microspores seen on the right side, B and D on the ventral face; A and B show the formation of the antheridium, $ 8 its dorsal cells, & /9 its ventral cells, C and D the formation of the antherozoids, /9 and S have disappeared : 7/ is the vegetative cell (prothallium of Millardet); a—^"development of the antherozoids {A—*D and a—d X580, e andy^X 700}. remains sterile, and may be considered a rudimentary prothallium; while from the others originate the mother-cells of the antherozoids, and these may therefore be looked on as a rudimentary antheridium.* The microspore of Isoetes lacustris breaks up, after hibernation, into a very small sterile cell and a large one comprising the whole of the rest of the
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1882
