20 BRITISH MARINE ALGA. 
and branches are soft and pliable, and are invested with a sort of slimy 
gelatine very similar to the viscid animal coating of living sponges. 
Indeed, it is owing to this peculiar feel of the frond that the genus was 
named from the Greek, x#dsov, or skin of an animal. The illustration 
shows the mode of growth in a frond of C. tomentoswm. The branches are 
generally divided in a dichotomous manner; in other words, regularly 
forked up to the tips of the divisions, and sometimes the branches throw 
out here and there short lateral ramuli or branchlets. The structure of 
this plant is entirely filamentous, the centre being composed of long string- 
like colourless filaments or fibres, while those which radiate horizontally 
around them are club-shaped, of a dark green colour, and invested with a 
thin layer of colourless slime. Dark green vesicles containing the fruit of 
the plant are borne on the sides of the club-shaped filaments. In mounting 
this species on paper, care must be observed that heavy pressure be avoided 
Fig. 22. Codiuwm tomentosum. Fig. 23. Vaucheria clavata. 
until the water is all drained out of the frond, otherwise it will adhere to the 
linen covering, or break off in pieces, and the specimen will be destroyed. 
The genus Vaucheria, named in honour of M. Vaucher, a distinguished 
French botanist, contains a few very interesting but minute green plants, 
and were it not for the dense masses in which most of the species grow, 
they would be constantly overlooked or disregarded. Some of them are 
parasitic on other larger algw, but they are more generally found on the 
muddy sea-shore, or on mud-covered rocks flooded by the tide. The 
species named Vaucheria velutina, is a summer annual, and consists of a 
dense mass of branching filaments, colourless below, but above, of a 
fine green, and of a delicate velvety texture. The branches, which are 
most intricately interwoven, throw up their little green tips an inch or so 
above the surface of the mud in which they grow. The fructification 
consists of a dark-green mass of endochrome contained within a little 
stalked round vesicle, which sprouts from the side of the erect 
branches, a short distance below the tips. This is well seen in the 
