. A textbook of botany for colleges and universities ... Botany. 136 MORPHOLOGY vegetative tissue of more primitive gametophytes. The antheridium initial produces an antheridium with the usual jacket of sterile cells investing sperm mother cells (fig. 306). At maturity the jacket cells break down and the mother cells (with their sperms) are free in the general cavity of the microspore (fig. 307). The male gameto- phyte, therefore, is reduced to one vegetative cell and one anthe- ridium ; and encased by the old microspore wall it is carried to the megasporangium, in which the female gametophjrt
. A textbook of botany for colleges and universities ... Botany. 136 MORPHOLOGY vegetative tissue of more primitive gametophytes. The antheridium initial produces an antheridium with the usual jacket of sterile cells investing sperm mother cells (fig. 306). At maturity the jacket cells break down and the mother cells (with their sperms) are free in the general cavity of the microspore (fig. 307). The male gameto- phyte, therefore, is reduced to one vegetative cell and one anthe- ridium ; and encased by the old microspore wall it is carried to the megasporangium, in which the female gametophjrtes are developing. There the male gametophyte bursts through the microspore coat (fig. 307). The sperms are very small, with more or less spirally coiled bodies and two terminal cilia. Selaginella thus shares with Lycopodium and Phylloglossum the character of producing biciliate sperms, a type characteristic of bryophytes, and in strong contrast with the sperms produced by other pteridophytes. Female gametophyte. —The female gametophyte is much more ex- tensive than the male gametophyte, but the greater part of it is in- vested by the old megaspore wall (fig. 308). The nucleus of the megaspore begins a series of divisions that continue until a large number of free nuclei are produced. This free nuclear division occurs chiefly in the apical (pointed) end of the megaspore, and results in a layer of nuclei, which later become invested by walls. Subsequent divisions result in a cushion of cells at the apex of the mega- r ^j^jj^ ^^^ ^ ^. ^j ^^^ ^ of Selaginella: the apical cushion ^ '_ o j o of ceUs having broken through the spore is free from cells, acting as a great heavy megaspore wall; an arche- food reservoir (fig. 308). The wall of -IZ M^°™''" ""' ^^''' ^^^ megaspore cracks at the apex and the apical tissue protrudes, developing a more or less expanded mass of tissue in which archegonia develop (figs. 308, 309). Later, the deeper
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbotany, bookyear1910
