If the allied group of the Coleochaeteae is considered together with the Florideae, we find a transition between the ordinary case of Coleochaete and that of Dudresnaya.  In Coleochaete, the male cell is a round spermatozoid, and the female cell an oosphere contained in the base of a cell which is elongated into an open and hair-like tube called the trichogyne.  The spermatozoid coalesces with the oosphere, which secretes a wall, becomes surrounded with a covering of cells called a cystocarp, which springs from cells below the trichogyne, and after the whole structure falls from the parent plant, spores are developed from the oospore, and from them arises a new generation.

In Dudresnaya, on the other hand, the spermatozoid coalesces indeed with the trichogyne, but this does not develop further.  From below the trichogyne, however, spring several branches, which run to the ends of adjacent branches, with the apical cells of which they conjugate, and the result of this conjugation is the development of a cystocarp similar to that of Coleochaete.  The remarkable point here is the way in which the effect of the fertilizing process is carried from one cell to another entirely distinct from it.

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 algae 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 aecidium spore.  These aecidium 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 aecidium generation.

Thus we have the series A.B.B.B ...  BCA