Thus I have endeavored to sum up the processes of asexual and of sexual reproduction. But it is a peculiar characteristic of most classes of plants that the cycle of their existence is not complete until both methods of reproduction have been called into play, and that the structure produced by one method is entirely different from that produced by the other method. Indeed, it is only in some algæ and fungi that the reproductive cells of one generation produce a generation similar to the parent; in all other plants a generation A produces are unlike generation B, which may either go on to produce another generation, C, and then back to A, or it may go on producing B's until one of these reproduces A, or again it may directly reproduce; A. Thus we have the three types: 1. A-B-C.--A-B-C.--A..................... etc. 2. A-B-B.--B-B...................B--A ... etc. 3. A B A B A............................. etc. The first case is not common, the usual number of generations being two only; but a typical example of the occurrence of three generations is in such fungi as _Puccinia Graminis_. Here the first generation grows on barberry leaves, and produces a kind of spore called an _æcidium spore_. These æcidium spores germinate only on a grass stem or leaf, and a distinct generation is produced, having a particular kind of spore called an _uredospore_. The uredospore forms fresh generations of the same kind until the close of the summer, when the third generation with another kind of spore, called a _teleutospore_, is produced. The teleutospores only germinate on barberry leaves, and there reproduce the original æcidium generation. Thus we have the series A.B.B.B ... BCA In this instance all the generations are asexual, but the most common case is for the sexual and the asexual generations to alternate. I will describe as examples the reproduction of a moss, a fern, and a dicotyledon. In such a typical moss as Funaria, we have the following cycle of developments: The sexual generation is a dioecious leafy structure, having a central elongated axis, with leaves arranged regularly around and along it. At the top of the axis in the male plant rise the antheridia, surrounded by an envelope of modified leaves called the perigonium. The antheridia are stalked sacs, with a single wall of cells, and the spiral antherozoids arise by free-cell formation from the cells of the interior. They are discharged by the bursting of the antheridium, together with a mucilage formed of the degraded walls of their mother cells.