. Biology and human life. Biology. 44 BIOLOGY AND HUMAN LIFE. Fig. 19. Fertilization in a flower When a pollen grain, p, alights on the moist sur- face of a stigma, s, it absorbs water and puts forth a thread of protoplasm, or a pollen tube, pt, which grows down the style into the ovary. The tip of the pollen tube finds its way to the inside of the ovule, 0, through a small passage- way, the micropyle, m. The large cell in the middle of the ovule, called the embryo sac, es, undergoes a number of changes which result in producing several nuclei. One of these nuclei at the end nearest the microp
. Biology and human life. Biology. 44 BIOLOGY AND HUMAN LIFE. Fig. 19. Fertilization in a flower When a pollen grain, p, alights on the moist sur- face of a stigma, s, it absorbs water and puts forth a thread of protoplasm, or a pollen tube, pt, which grows down the style into the ovary. The tip of the pollen tube finds its way to the inside of the ovule, 0, through a small passage- way, the micropyle, m. The large cell in the middle of the ovule, called the embryo sac, es, undergoes a number of changes which result in producing several nuclei. One of these nuclei at the end nearest the micropyle corresponds to an egg cell. Similar divisions take place in the nucleus of the pollen grain, and one of the re- sulting nuclei corresponds to a sperm cell. The cell walls separating the pollen tube and the em- bryo sac dissolve, and the pollen nucleus unites with the egg nucleus. The newly formed joint nucleus, or fertilized egg, begins to divide. Thus it develops into a new plant, or embryo; the ovule containing it becomes a seed; the ovary becomes a fruit which can be seen only with the microscope (see 7, Fig. 32). This pollen tube grows through the style and into the hol- low of the ovary, then through a small hole in the ovule, the micropyle, which means "smallgate- way" (see in, Fig. 19). Finally it reaches the central space of the ovule, where there is a special mass of jelly like living stuff, the embryo sac (see es, Fig. 19). Here a portion of the matter in the pollen tube unites with a portion of the matter in the em- bryo sac, and from this united mass a new plant begins to develop. The uniting of the two masses of living matter is now called fertilization. This is the real act of repro- duction, for its result is in fact a new individual (see Fig. 19). 36. Seed and fruit. After fertilization takes place the mass in the em- bryo sac absorbs food in large quantities from the parent plant and becomes. Please note that these images are extracted from scanne
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