the Cystocarp in Rhodymeniales. 361 
between the carpogonium and these auxiliary cells being 
effected by distinct ooblastema-cells. 
Ceramium tenuissimum, J. G. Ag. 
As is well known from Janczewski’s description (’ 76 ), the 
genus Ceramium presents a case which contrasts in an 
interesting way with that presented by Callithamnion . While 
in Callithamnion the procarps consist of one carpogonial 
branch with two auxiliary cells, in Ceramium it consists of 
one auxiliary cell and two carpogonial branches. Both are 
equally specialized divergences from the more primitive type, 
but in quite different directions. 
The plant whose procarp I have figured (PL XVIII, Fig. 19) 
is, I believe, Ceramium tenuissimum , J. G. Ag., a very delicate 
diaphanous species. I neglected, however, to collect tetra- 
sporiferous plants, by which the plant is more readily distin- 
guished from its congeners. From the figure it will be seen 
that the auxiliary cell is not, as Bornet and Janczewski have 
supposed, the mother-cell of the two carpogonial branches, 
but a later-formed superior cell. The branches are 4-celled, 
as is very generally the case in Ceramiaceae. The trichogyne 
has been shut off in the procarp on the right in the figure, and 
the remains of the ooblastema-tube by which the carpogonium 
and the auxiliary cell had been put in connexion was seen as 
represented. No conjugation seems to have taken place in 
the case of the second carpogonium. 
The case of Ceramium , apart from the duplication of the 
carpogonial branches, is again very similar to the primitive 
condition described for Antithamnion Plumula . 
Ptilota plumosa, C. Ag., and Plumaria elegans, Bonnem. 
Plumaria elegans is the Ptilota sericea of the Phycologia 
Britannica, and resembles Ptilota plumosa so much that, as 
Harvey tells us, it was at first often considered a shallow- 
water form of that species. With closer observation it was 
