. Botany of the living plant. Botany. POLLINATION AND FERTILISATION 271 chalazogamy. Sometimes an irregular course may be pursued, by traversing the integuments, as in the Elm. But here the course appears to be very inconstant. It is doubtful whether these irregularities have any si)ecial significance, but it is worthy of remark that they occur in relatively primitive Families of Flowering Plants. The pollen-tube on entering the micropyle conveys with it tlie two male gametes enclosed in the cytoplasm of the tube (Fig. 213, A). Probably the turgor of the contents has its effect in rupturing th
. Botany of the living plant. Botany. POLLINATION AND FERTILISATION 271 chalazogamy. Sometimes an irregular course may be pursued, by traversing the integuments, as in the Elm. But here the course appears to be very inconstant. It is doubtful whether these irregularities have any si)ecial significance, but it is worthy of remark that they occur in relatively primitive Families of Flowering Plants. The pollen-tube on entering the micropyle conveys with it tlie two male gametes enclosed in the cytoplasm of the tube (Fig. 213, A). Probably the turgor of the contents has its effect in rupturing the soft tip of the tube, and extruding its contents. The nuclei of the two gametes can shortly afterwards be recognised in the embryo-sac. The one passes into the ovum and fuses with its nucleus. The result of fusion of the male and female gametes is the zygote. The other passes on to the central fusion- nucleus and coalesces with it (Fig. 214). The mechanism of the movements within the embryo-sac is uncertain. It has been suggested that protoplasmic streaming may assist it. On the other hand, the peculiar form which the male nuclei sometimes take suggests indepen- dent movements, hke those of the sperms of lower plants to which they correspond functionally. Meantime the synergids shrivel, and begin to- disorganise. Clearly their function is completed on fertilisation. In the case of Lilium the more or less spiral form of the male nucleus, when it penetrates the ovum, has been seen to be retained till it is applied to the nucleus of the ovum. But the nuclei gradually become alike in shape, size. and structure. Both are in the resting condition, and have a nucleolus (Fig. 215). The nuclear membrane then disappears at the place of contact, their cavities become one, the chromatin-reticulum of the one unites with that of the other, and the resulting fusion-nucleus can scarcely be distinguished from the nucleus of an unfertiUsed egg. Finally the nucleoli fuse also. The details of th
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