SECT. n. CALLITHAMNION. 231 



broad bases radiate from the centre, and other arrange- 

 ments occur. 



The Bhodosperms are comparatively small plants. 

 Some which form velvety cushions on stones, or minute 

 tufts on small Algae, are only the fraction of an inch 

 high, but the larger kinds range from one to four, six, 

 ten, or twenty inches ; probably none exceed two feet. 

 In thickness, some fronds are fine, like jointed and 

 branched hairs, while others are thick, like hog's bristles 

 or crow quills. Numerous as the forms are, the simple 

 jointed filamentous frond is connected by a series of 

 forms with the highest order of the class. 



A great portion of the Rhodosperms on the British 

 coasts is composed of the exquisitely beautiful order of 

 the Ceramiacese. They abound in every rocky pool, on 

 every piece of wood that has been long exposed to the 

 waves, on rocks and stones, and, above all, they fringe 

 the Zostera marina, or sea wrack, as well as the firmer 

 Algae, with every shade of red from bright crimson to 

 purple. They are articulated filiform plants, approaching 

 in simplicity of form to the Confervas. The genus Calli- 

 thamnion, which has thirty species in the British seas, 

 consists of cylindrical jointed threads more or less 

 profusely branched, and distinguished by having the 

 divisions between the joints, opaque and of various 

 shades of red and purple, while the joints themselves 

 are transparent and colourless, so that the stein and 

 branches appear to be striped across by alternately white 

 and coloured bands which are often visible to the naked 

 eye, notwithstanding the smallness of the plants and 

 the delicacy of their filaments, as the C. sparsum, 

 which is a soft purple tuft of jointed threads scarcely 

 one-tenth of an inch high. 



The Callithamnion corymbosum has a soft jointed fila- 

 mentous stem, hair-like below, fine as a cobweb above, and 

 excessively branched, with dichotomous branches. In 



