374 



THE SEA SHORE 



P. Brodicei is moderately common on our coasts. This is a large 

 brown species, with seven siphons surrounded by a thick cellular 

 layer which conceals the articulations and is too opaque to allow 

 the siphons to be seen without dissection. Its branches, which are 

 alternate, bear short tufts of delicate branchlets. 



FIG. 257. Polysiphonia parasitica FIG. 258. Polysiphonia Brodiai 



P. byssoides, so called on account of the pink filaments that 

 fringe the fronds, has also seven siphons. It is a large and beau- 

 tiful weed, moderately common on our coasts, of a bright-red 

 colour, with conspicuous fructification. The branches are alternate, 

 and the branchlets are clothed with the byssoid filaments above 

 referred to. 



P. violacea is of a reddish-brown colour, with long silky alter- 

 nate branches, and four siphons. It receives its specific name from 

 the fact that it turns to a violet colour when dried. 



P. nigrescens has, as the specific name implies, blackish fronds, 

 and these are freely branched. The 

 tubes, about twenty in number, are 

 flat, and are arranged round a large 

 central space. 



Our last example P. atro-rubes- 

 cens is of a dark reddish-brown 

 colour, with rigid and densely-tufted 

 fronds. It has twelve tubes, arranged 

 spirally round a central cavity. It is common in the lower rock 

 pools of some coasts. 



In the same order we have the genus Chondria, so called on 

 account of the cartilaginous nature of its thread-like fronds. These 

 are pinnately branched, and the club-shaped branchlets taper below. 

 The main stem is jointed and contains many siphons. The genus 



FIG. 259. Polysiphonia 

 nigrescens 



