36 BRITISH MARINE ALG. 
of the tubercled receptacle which contains the spores, and is itself com- 
posed of very compact cellular tissue. Professor Agardh includes this 
species with some others in a group which he calls Fucodiwm, but 
at present I have thought proper to describe it under its generally 
known name. 
The genus Cystosetra contains some species which are tolerably 
abundant, at least on the southern coasts of Britain. The generic 
name of this group indicates a chain of cysts or bladders, of which 
the branches of all these plants are chiefly composed. The roots of 
all are thick and woody, the, stems are short and cylindrical, and are 
beset on all sides by numerous slender branches variously divided 
and clothed throughout with little spine-like ramuli. In our illustra- 
tion of the species, C. ericoides (Fig. 40), which is very heath-like 
(whence its specific name), the air-vessels are very small and are pro- 
duced near the tips of the branches. The receptacles are also terminal 
and spiny. The fronds are from Ift. to 2ft. high, and when seen 
growing in shallow pools with the sun shining full upon it, the whole plant 
is beautifully iridescent. Young collectors who see this brilliant alga for 
the first time, are naturally enchanted with the exquisite glaucous tints 
which it reflects, but their delight is quickly dispelled, for upon removal 
from the water, it is found to be of a dull brown olive, all the full rich 
tints of blue and green, more like the phosphorescent gleams that flash 
from some of the marine animals than any vegetable colours, vanish 
the moment the plant is removed from its native element. OC. fibrosa, 
Fia. 40. Cystoseira ericoides. Fig. 41. Cystoseira fibrosa. 
very well represented in Fig. 41, is a handsome and very well marked 
species. The air-vessels are larger than in any other British species, and 
are produced in succession along the branches, but at some distance from 
