. A manual of botany. Botany. ANGIOSPEEMiE 183 Fig. 935. ' whicli descended to help form the definitive nucleus, is the female gamete, or oosphere, while the other two are known as the aynergidce. In some few cases the definitive nucleus is consti- tuted by only the one from the chalazal end ; there are then two oospheres, of which only one becomes fertilised. In rare cases the synergidse are fertile gametes, though this very seldom happens. At this stage the development of the prothallium remains suspended, and nothing further takes place unless the oosphere becomes fertilised. The egg appara
. A manual of botany. Botany. ANGIOSPEEMiE 183 Fig. 935. ' whicli descended to help form the definitive nucleus, is the female gamete, or oosphere, while the other two are known as the aynergidce. In some few cases the definitive nucleus is consti- tuted by only the one from the chalazal end ; there are then two oospheres, of which only one becomes fertilised. In rare cases the synergidse are fertile gametes, though this very seldom happens. At this stage the development of the prothallium remains suspended, and nothing further takes place unless the oosphere becomes fertilised. The egg apparatus lies almost always immediately below the micropyle, and is thus not covered by a mass of tissue as in the Q-ymno- sperms. The pollen tube reaches the micropyle as already described; its apex becomes more or less muci- laginous, as does the wall of the embryo sac, and one of the male gametes makes its way throiigh to the oosphere, with which it fuses, nucleus with nucleus and protoplasm with pro- toplasm. The fertilised oosphere, now become a zygote, surrounds itself with a cell-wall, and the synergidae become disor- ganised and disappear. The further fate of the zygote differs in the two classes into which the Angiosperms are divided and will be discussed later. The embryo sac becomes filled with a tissue known as the endo- sperm, which has, however, a different morphological yalae from the tissue in the maorospore of the Gymnosperms, though it bears the same name. This so-caUed endosperm is derived from the definitive nucleus of the embryo sac. This body divides repeatedly, form- ing a number of nuclei which become disposed in a layer all over the surface of the wall of the embryo sac. Round each of these an aggregation of protoplasm takes place, so that the sac. Fig. 935. Macrosporajigium (ovule) of an Angiosperm. mac. Maorospore. oos. Oosphere. Please note that these images are extracted from scanned page images that may have been digitally enhanced fo
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectbotany, bookyear1895
