in all directions. The archegonia are microscopic flasks, each containing an egg-cell or oösphere; they are entered by one or more of the locomotive antherozoids, which coalesce with the egg-cell; the latter is thereby fertilized, and soon grows by cell division into a plant resembling that from which the spores were originally obtained. The life-history of a vascular cryptogam is, so to speak, a story completed in two volumes. Microscopic research has revealed a most interesting relationship between flowering plants and the heterosporous cryptogams. When the development of a pollen grain in the anther of an ordinary flower is studied and compared with that of a microspore, the two are found to agree in a remarkable manner. The sporangium corresponds in all essential points with the pollen-sac, and its generatic tissue develops in similar fashion to that from which the pollen grains originate. In both cases an archesporium is produced by the division of a hypodermal cell; this tissue next divides into a tapetal layer and a row of mother-cells; the tapetal layer dissolves, isolating the mother-cells, each of which then forms in its interior four daughter-cells, which are the spores or pollen grains, as the case may be. Not only are the antecedents of microspores and pollen grains alike, but their subsequent histories offer many points of resemblance. Pollen grains are known in numerous instances to form in their interior one or more vegetative cells, which can hardly be regarded as other than a rudimentary male prothallus, such as is commonly developed by a microspore.