236 
THALLOPHYTES. 
But on the other hand the formation of oospores exhibits a certain resemblance 
to the process of conjugation. It is distinguished from that of the Pandorinese in 
this point of importance only, that the two coalescing sexual cells are not alike, 
so that the fertilisation of Vaucheria and (Edogonium may be considered as a 
higher form of conjugation from a morphological point of view. But the mode 
of formation of many oospores displays also a greater or less resemblance to the 
mode of fertilisation which we shall describe as a third type; and in this respect 
the Saprolegnieae in particular present a similarity to certain Ascomycetes. 
3. Formation of Carpospores in Carpogonia. This type resembles the second 
in the fact that the two sexual organs contribute in very different degrees to the 
production of the fertilised body, the male organ only inciting to change, while 
the whole of the further development of the plant proceeds from the female organ, 
the result being the production of the Sporocarp. 
The female organ, which may consist either of one cell or of more, may be 
designated by the general term Carpogomum. The male organs vary greatly 
according to the group to which the plant belongs; they may be swarming or 
passively motile antherozoids, or tubular Pollinodia ; and fertilisation may be 
effected by the entrance of the antherozoids, as in the case of oospores, or by a 
kind of conjugation, the sexual cells coalescing by means of openings in the cell- 
walls of both, or finally by simple apposition and probably diffusion of a fertilising 
substance. The product of fertilisation is sometimes a single cell germinating 
directly or through the medium of zoospores ; but more generally a multicellular 
body results, from which spores are finally produced. An alternation of generations 
may here also be recognised, rudimentary or more fully developed according as the 
structure of the fructification is simpler or more complicated. In the simplest 
cases the sporocarp appears only as an appendage of inconsiderable size to the 
plant ; in the other extreme the fructification is able to continue an independent 
growth for a considerable time, and thus constitutes a second alternating genera- 
tion. These phenomena will be described more in detail in the special description 
of the Carposporeae. One essential difference between sporocarps and oospores 
consists in this, that in the production of the former certain cells also take part 
which were not immediately concerned in the act of impregnation; and that, with 
the exception of the simplest cases, the portion of the fructification which produces 
the spores is surrounded by a sterile envelope which serves merely for protection 
or also for further nourishment. Fig. 164 illustrates some of the most different 
forms of sporocarps. 
In ColeochcBte {A) the female organ or carpogonium (hitherto described as the 
oogonium) consists of a single cell w which runs out upwards into a long narrow 
canal opening at the apex. Fertilisation is effected by small roundish swarming 
antherozoids m, and as a consequence the portion of the protoplasm (oosphere) 
which occupies the basal part of the cell becomes invested with a firm cell-wall. So 
far the phenomena are the same as in the formation of the oospores of Vaucheria 
or (Edogonium^ the only important difference consisting in the long canal formed by 
the cell-wall. A more essential deviation is now manifested in that the body which 
previously had the appearance of an oospore grows considerably after fertilisation, 
and in the fact that the effect of fertilisation shows itself also in the growth of the 
