hed alg^. 151 



is not uhlike an enlarged, exaggerated, and very spiney 

 P. Harveyi. Unlike P. elongata, tlie branches are 

 robust, somewhat bent at various sliarp turns and 

 angles, and the parts rapidly diminish in size from base 

 to apex, as they throw out branches and branchlets. 



POLYSIPHONIA NIGRESCENS,* GrEV. 



This is an extremely variable plant, not uncommon 

 along our whole east coast, and identified by one 

 or two distinguishing marks. It is a perennial and 

 grows in rock pools and deep water. It is almost 

 quite black, or very dark brown, when mounted and 

 dry. It has a leading stem, though this is not always 

 easy to make out ; it may, however, usually be detected, 

 as more or less prominent. It is not commonly larger 

 than a bristle. A microscopical dissection of it, shows 

 it to consist of from twelve to eighteen tubes, arranged 

 around a central tube, a singular diversity of habit 

 in a species whose generic congeners are generally 

 so constant to their type, in this respect. Harvey says 

 the best general marks of the species are its many 

 tubed internodes of moderate length, easily visible 

 with a lens ; and its decompound regulatiy pinnate 

 method of branching. The branches divide and sub- 

 divide, alternately twice or thrice in a very regular 



* Nigrescens = black. 



