360 THE SEA SHORE 



rosy, jointed fronds, with the ultimate divisions of the branches 

 disposed in a level-topped (corymbose) manner, growing on rocks 

 and weeds near low-water mark ; C. polyspermum, growing in 

 globular tufts on Fucus serratus and F. vesiculosus, with short awl- 

 shaped pinnules, and closely-packed clusters of spores ; C. HooJceri, 

 with opaque stem and branches, and spreading branchlets that are 

 themselves branched, and bear spreading plumules at their tips ; 

 and C. arbuscula, found on the west coasts, with a stout stem, naked 

 below, and having a very bushy habit. 



It is often by no means an easy matter to distinguish between 

 the different species in such a large genus as Callithamnion, and 

 we strongly recommend the beginner to first stul^r the charac- 

 teristics on which the classification of the Algce is based, and to 

 arrange his specimens according to the orders and genera to which 

 they belong ; and then, after mastering the principles of classifica- 

 tion, he should refer to one of those larger works in which all known 

 British species are described, and make himself acquainted with the 

 features of each individual species in his collection. 



Before leaving the present genus we ought also to mention the 

 fact that many of the species lose their natural colour rapidly 

 when placed in fresh water ; hence when they are being cleansed 

 for mounting salt water should be employed. Further, even after 

 they have been satisfactorily mounted, they are liable to be spoiled 

 if left exposed to moist air. The salt water used need not be the 

 natural sea water ; a solution of common table salt, made up to 

 approximately the same strength as sea water, will answer the 

 purpose just as well. 



The genus Griffithsia includes some very beautiful weeds of deli- 

 cate threadlike structure and of a fine rose colour. The frond con- 

 tains a single tube, and is jointed and forked, the joints being 

 usually transparent. The spore clusters are enclosed in a gelatinous 

 sac surrounded by a whorl of little branchlets, the spores themselves 

 being minute and angular. The tetraspores are attached to the 

 inner side of whorled branchlets. 



The commonest species is G. setacea, which is of a bright-red 

 colour and slightly branched. It is also of a somewhat firm structure, 

 but soon loses both firmness and colour when removed from salt 

 water ; and, like Callithamnion, rapidly fades if put into fresh water, 

 which is readily absorbed through its membranes, causing them 

 to burst and discharge their colouring matter. It receives its 

 specific name from its bristle-like forked fronds. G. secundiflora is 



