The gradual change of structure from the lowest to the highest cryptogamic form is accompanied by a singular variety in the mode of reproduction, and a degree of vital energy scarcely to be expected, at least in beings of such low organization as the yeast plant, which produces gemmæ in vast and rapid profusion, each gem or bud being only a facsimile of the parent cell. In like manner the mother plant is reproduced by the germination of the green zoospores, the green globular cells in the fronds of the lichens, the motile gonidia, and the discs in the baskets of the Marchantia, especially those of the Marchantia polymorpha, which have such vigorous vegetation that they form stomates on whichever side is turned to the light, and roots on the other. The result of all these is an individual perfectly similar to its parent, like that produced by a bud and cutting of a tree, or the axillary fruit buds of the Begonia. The leaves of that flowering plant, as well as those of the Achimenes and Gloxinia, possess the property of reproducing the parent plant, for, when laid on moist earth and slit in different places, a young plant rises from the upper side of the fracture, and roots shoot down from the under. Although this manner of growth resembles the germination of the embryo of an archegonium, it is widely different, for the embryonic cell is fertilized by the spermatozoids, so there is a certain analogy but not the smallest affinity. The highest vegetable classes can reproduce the mother plant in many ways, but they have nothing akin to the alternation of generations exhibited by many of the lower tribes, nor yet to conjugation like the Desmidiaceæ and Diatoms. Possibly the spores resulting from these two modes of reproduction, as well as the resting spores, may produce new species; certainly those resulting from fructification do occasionally yield new varieties.