. Botany for high schools and colleges. Botany. 420 BOTANY. A). In their development most ovules, althougli straight (Fig. 306, A) at first, become afterward more or less curved upon themselves (Fig. 306, B and 0). The development of the embryo sac takes place in a much simpler way in Angiosperms than in Gymnosperms.* An axial cell enlarges greatly, becoming thus the young embryo- sac (Fig. 306, em). In preparation for fertilization, it divides into a row of several (3-6) cells, the uppermost of which forms four nuclei, one of which becomes the germ-cell. By the absorption of the cell wall, th
. Botany for high schools and colleges. Botany. 420 BOTANY. A). In their development most ovules, althougli straight (Fig. 306, A) at first, become afterward more or less curved upon themselves (Fig. 306, B and 0). The development of the embryo sac takes place in a much simpler way in Angiosperms than in Gymnosperms.* An axial cell enlarges greatly, becoming thus the young embryo- sac (Fig. 306, em). In preparation for fertilization, it divides into a row of several (3-6) cells, the uppermost of which forms four nuclei, one of which becomes the germ-cell. By the absorption of the cell wall, the upper cell fuses with the second (which mayor may not contain four nuclei), forming a common cavity containing many nuclei or young. Fig. 306—Diagrammatic longitudinal Bections of ovules. A, the straight ovule (or- thotropoiif); *, the body of the ovule, with its embryo sac, em ; al, the outer ovule coat (primine); ii, the mner coat (sc-cundine); m, the micropyle ; c, the base of the ovule, where the coats arise, called also the chalaza;,/", the ovule stalk or funiculus. ^,an inverted ovule (anatropous); the long funiculus,/, has fused with theprimine of one side of the ovule and formed the raphe, r. C, a bent ovule (campjlotropous).— After Prantl. cells, several of which, including the Germ-Cell^ remain at the top, the others (Antipodal Cells) occupying the lower part. No endosperm is to be seen at this stage, f The fertilization of the germ-cell involves two operations, Pollination—, the deposition of the pollen upon the stigma, and Fertilization proper. * See " Nouvelles Reclierohes sur le developpement du sac embryon- naire des Phanerogames angiospermes," by Julien Vesque, in Annates des Sciences NaturdUs, 1879. f The endosperm, which here forms after fertilization of the germ- cell, may be regarded as a belated piothallium. It is here no longer necessary for the prothallium to precede the formation of the germ- cell ; there is consequently
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectbotany, bookyear1888
