222 BRITISH SEA-WEEDS. 



thrice dichotomous. Favellae unknown; tetraspores borne on 

 short stalks in the axils of the branchlets. 



This species is not uncommon on the south and west 

 shores of England and Ireland, but is more rare further 

 north. It grows on rocks and submerged woodwork, or 

 in deep water, and is annual. It adheres closely to paper, 

 and is very beautiful when dry ; but specimens gathered 

 in autumn are frequently covered with Diatomacese, and 

 have not the bright colour which characterizes the plant 

 in summer. 



Genus CIII. CALLITHAMNIOW. 



Eronds thread-like, branched, jointed, one-tubed ; the 

 stem and branches in some species made opake by the de- 

 velopment of decurrent fibres in the walls of the primary 

 cells. Spores angular, contained in a transparent envelope, 

 in favellae, which are generally in pairs, stalked or axillary 

 on the branches ; tetraspores tripartite or cruciate, oblong 

 or globose, naked, sessile or stalked, distributed among the 

 branches. — Callithamnion, from the Greek katos, beau- 

 tiful, and thamnion, a little shrub. 



More than a hundred species are included in this 

 genus, and about a quarter of the number are natives of 

 our shores. They are, with one or two exceptions, of 

 small size, and some of them so tiny as to be scarcely 

 visible to the naked eye. The genus is variously sub- 

 divided by different writers, some of whom go so far as 

 to arrange its constituents in three separate genera. I 

 have adopted the principal sections used by Professor 

 Agardh, which are at the same time simple and sufficient 

 for the purposes of a popular work. Nearly all the 



