Phanerogams
(see Ovule and Pollen). The homologous stages, or what are at present regarded as such, may be briefly stated as follows. In Phanerogams, the pollen grains represent the microspores, and the multicellular nature of the pollen corresponds to the multicellular microspore of Selaginella, with its rudimentary Prothallus represented by the vegetative cell. The Gymnosperms and the Angiosperms differ as regards the ovule. In Gymnosperms, the temporary endosperm is regarded as representing the Prothallus inclosed in the embryo-sac as its macrospore; the corpuscula represent archegonia, the rosette cells represent the neck of the archegonium, and the central cell of the corpusculum represents the oosphere. As already stated, the large-celled tissue in the macrospore of Selaginella is regarded by Pfeffer and Sachs as representing the endosperm that develops in seeds after fertilisation. In Angiosperms, the embryo-sac represents the macrospore, the antipodal cells, perhaps, correspond to the Prothallus, the embryonal vesicle to the oosphere, the helper-cells to the neck of the archegonium, and the endosperm has the significance already stated.