. An introduction to vegetable physiology. Plant physiology. 440 VEGETABLE PHYSIOLOGY opens a little at the apex when the archegonia are mature, in order that fertilisation may be possible. When we pass to the Spermophytes two further advances may be seen. The spore never escapes from the sporangium, and the prothallium does not emerge even in part from the spore, which does not open. In these plants the megaspore is represented by the cell known formerly as the emhryo-sac, the sporangium being the ovule. Among the Spermophytes we have two types of prothallium which are characteristic. Fia. 17
. An introduction to vegetable physiology. Plant physiology. 440 VEGETABLE PHYSIOLOGY opens a little at the apex when the archegonia are mature, in order that fertilisation may be possible. When we pass to the Spermophytes two further advances may be seen. The spore never escapes from the sporangium, and the prothallium does not emerge even in part from the spore, which does not open. In these plants the megaspore is represented by the cell known formerly as the emhryo-sac, the sporangium being the ovule. Among the Spermophytes we have two types of prothallium which are characteristic. Fia. 177.—Geemikation of Meqaspoee of Sdagindla. arch, archegonia; 008, oospheres ; em', embryo. The spore has been ruptured and the upper portion removed. of the Gymnos'perms and the Angios'perms respectively. Pig. 178 shows the structure m the former ; the spore or embryo-sac is filled with the prothalUum, formerly called the endosperm, at the apex of which are several archegonia, each containing a female gamete or oosphere. After fertili- sation the resulting zygote gives rise to a young sporophyte or embryo, which becomes embedded in the endosperm. The structure thus formed consisting of the sporangium or ovule, with the solitary spore it contains, the latter having in its interior the embryo surrounded by the prothallus, constitutes the structure loiown as the seed. It becomes. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Green, J. Reynolds (Joseph Reynolds), 1848-1914. London, J. & A. Churchill
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