192 BRITISH MARINE ALGA. 
little round masses, called favelle, which contain the spores of this 
plant, are produced on the sides of the lateral branchlets, and are sup- 
ported, or partly embraced, as it were, by two or three short ramuli. 
In the living state, or before the plant is mounted on paper, these favellz 
are seen to have a pellucid limbus or border, through which, under the 
microscope, a multitude of minute angular spores are distinctly visible. 
The colour of the plant is properly a clear red, but itis found often enough 
of a brownish tint, sometimes yellowish, and even of as dark a colour 
as Polysiphonia nigrescens (Fig. 102). Plants having the latter tint are of 
the common coarse variety which I have frequently taken at Brighton, 
growing among the fuci or rock-weeds about haif-tide level, the fronds 
of which were often over 20in. long. 
The tetraspores of this species, as in most of the Ceramiee, are 
generally formed from the surface cellules, and are immersed in the 
articulations, but in some they project slightly above the surface, like 
little pimples. One of the most distinct varieties of this species, formerly 
C. botryocarpum, from the grape-like form of its clustered spore-vessels, 
is now known as C. rubrum, var. proliferum, the branches of which are beset 
on all sides with short simple or sparingly branched ramuli, the tips of 
which are straight or pointed, those of C. rubrum being slightly hooked 
inwards. Sometimes this variety produces globular favelle; but its 
distinctive fruit vessels are the clustered masses which are borne on the 
lateral branchlets, but which are not accompanied by involucral or 
clasping ramuli. This, like most of the other species, is a summer annual. 
The colour is rarely so bright a red as that of the foregoing plant, but the 
whole surface of the fronds is coated with cellules, which are sometimes 
purplish, but often change to a greenish yellow. 
The only other variety of C. rubrum which I think it necessary to 
describe is the plant which was figured by Dr. Harvey the under 
name of C. decurrens. It is now regarded by Professor Agardh as a 
variety of C. rubrum; it may be known by its slender fronds, which 
are much more sparingly branched, and by the presence of a narrow 
colourless space which occurs in the centre of the dissepiments or in- 
ternodes, which is caused by the faint tint or even absence of coloured 
cellules. An ordinary lens will readily show the surface cells of these 
plants when they are gathered fresh from the sea; and in the absence of 
fruit, the presence of these cells in all parts of the stems and branches, 
afford the student a ready means of recognition, although, of course, 
it requires practice and experience to distinguish the numerous forms of 
this variable species. The only plant with which C. botryocarpum (or 
proliferum) is likely to be at first confounded, is the curious species C. 
Deslongchampsii, the fruit of which is very similar, being produced in 
clusters, and, like the favelle of that species, equally destitute of 
involucral ramuli, as seen at a, Fig. 177. The colour of the joints of the 
stems and branches is, however, very different, being of a dark purple, 
nd the spaces between them are perfectly colourless; the tips of all 
