a neiv Genus of Endophytic Algae . 191 
formed, the exterior layer of the Cladophora cell-membrane 
being, of course, raised locally along with it. 
So far as I have observed there is not much difference in 
the form of the tetrasporic and cystocarpic sori, and it is 
sometimes rather difficult to say to which class a sorus should 
be referred, the long terminal cells of the central group of 
paraphyses in the tetrasporic sori somewhat resembling 
trichogynes. 
The tetrasporic sori are roundish in outline and are often 
scattered in great numbers over the surface of the thallus : 
the cystocarpic on the other hand are larger, more flattened, 
and not nearly so numerous, but I am not sure that these 
characters are constant. The central portion of each tetra- 
sporic sorus is occupied by a group of sterile filaments com- 
posed of from two to four short cells and an elongated terminal 
cell which is often very much attenuated upwards. The up- 
ward growth of this central group of paraphyses, which are 
always the first to be formed, locally raises and finally ruptures 
the exterior layer of the cell-wall of the Cladophora , the edges 
of the torn membrane, released from pressure, are turned back 
on to the surrounding membrane and form as it were a ring 
around the opening made by the paraphyses (Figs. 9 and 13). 
A mature sorus consequently resembles a conceptacle with a 
hyaline pericarp and a more or less prominent ostiole, the en- 
closing cell-wall being represented by the raised portion of the 
cell-membrane of the Cladophora , and the ostiole by the hole 
formed by the central group of paraphyses. The remaining 
filaments of the same sorus, with the exception of the outer- 
most or marginal row, are nearly all fertile. The shorter cells 
of the basal layer of the sorus lengthen and form short fila- 
ments, the terminal cells of which expand into at first oval then 
oblong sporangia, which, by transverse division of their con- 
tents, finally form two- or four-parted tetraspores — Dr. Bornet’s 
Cherbourg plants produced tetraspores (Fig. ri) ; my Torquay 
and Puffin Island ones bispores. Here and there between the 
sporangia an isolated filament remains sterile, and forms a 
paraphysis similar to those of the central bundle. As before 
