2.28 BRITISH SEA-WEEDS. 



the plumules, one or several on each ; some of them con- 

 tain eight grains, each of which, when ripe, becomes a tri- 

 partite tetraspore. 



This is a handsome, feathery plant, of a bright carmine 

 colour; it grows near low -water mark, is annual, fruits in 

 summer, and is rather rare. It may be readily distin- 

 guished by the long bare stem and simple pinnae of its 

 plumules. It is named in honour of Mr. Borrer, a well- 

 known botanist, by whom it was discovered. 



Callithamnion polyspermum. The many-spored 

 C alii thamni on . 



Fronds forming globular tufts one to three inches in 

 diameter, slender, delicate, much branched ; branches zig- 

 zag, of two or three series, plumulate from each joint ; 

 plumules alternate, pinnate, or rarely bipinnate; pinnae 

 alternate, short, simple, spine-like; articulations of the 

 branches four or five times, of the branchlets about twice 

 as long as broad. Favellae of large size, in clusters, on the 

 rachis of the plumules ; tetraspores tripartite, borne on 

 the inside of the pinnae of the plumules ; antheridia formed 

 of innumerable minute cells, strung together, occupying the 

 same position as the tetraspores. 



Although extremely delicate and slender, this plant 

 sometimes grows so abundantly on Fucus serratus and 

 Fucus vesiculosus as to completely cover their fronds. 

 It is one of the most common of the Callithamnia, and 

 may be found in summer in almost every locality round 

 our coasts. The short, awl-shaped pinnules of the plu- 

 mules are its most obvious character; but it is gene- 

 rally a variable plant, and must be carefully examined 

 under a microscope, in order to determine its identity. 



