RHODOMELACE.E. 99 



The more delicate species of this genus require to be, 

 laid down in salt-water, or they will lose their colour and 

 stain the paper on which they are dried. At certain periods 

 of their growth, particularly when nearly mature and in 

 fruit, they decay so quickly that it is necessary to lay 

 them out almost immediately after being gathered. 



Sttbdiyisiox 1. — Primary tubes more than four. 

 Polysiphonia Brodisei. Brodie's Polysiphonia. 



Fronds from six to twelve inches long ; stem composed of 

 an axis of seven primary and seven secondary tubes, sur- 

 rounded by a thick layer of smaller cells, which form a 

 bark, and hide the joints of the axis ; branches alternate, 

 furnished with numerous short tufts of delicate jointed 

 branchlets ; articulations rather longer than broad. Spores 

 in egg-shaped, short-stalked conceptacles ; tetraspores in 

 swollen branchlets. 



This large and handsome species grows on rocks and 

 corallines, near low-water mark. It is moderately 

 abundant in many localities, and thrives equally in 

 the comparatively cold climate of Scotland and in the 

 warmer latitude of the Channel Islands. It is annual, 

 and in perfection in summer. 



Polysiphonia nigrescens. Blackish Polysiphonia. 



Fronds shrub-like, from three to twelve inches or more 

 long, of very variable thickness, growing several from the 

 same base ; branches alternate, pinnate ; branchlets elon- 

 gated, awl-shaped, alternate ; tubes flat, about twenty in 

 number, placed round a large central cavity ; articulations 

 very short. Spores in broadly-ovate, stalkless conceptacles ; 

 tetraspores near the tips of the branchlets. 



Specimens of this species vary very much, according 



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