100 BRITISH SEA-WEEDS. 



to the season in which they may be gathered. In spring 

 and summer, the fronds have their full complement of 

 branchlets, and are in consequence light and feathery. 

 In autumn and winter, the more slender branchlets are 

 wanting, and the plant has a coarse, worn, and scrubby 

 appearance. This is not a diflBcult species to determine. 

 The numerous tubes and short joints of its stem are 

 characters whereby it may be readily distinguished. It 

 is perennial, and may be found at any season on almost 

 every part of our coast. 



Polysiphonia atro-rubescens. Dark-red Poly- 

 siphonia. 



Fronds erect, rigid, densely tufted, from three to twelve 

 inches long ; main branches forked, long, tapering ; branch- 

 lets alternate, short, spine-like, fastigiate, more or less 

 forkedly divided; tubes, about twelve, arranged spirally 

 round a small central cavity ; articulations, of the lower 

 part of the frond, about three times as long as broad, those 

 of the upper part about once and a half. Spores in broad, 

 wide-mouthed, short-stalked conceptacles ; tetraspores in 

 spindle-shaped branchlets. 



This species grows near low-water mark, and is mo- 

 derately abundant in many localities. It is annual, and 

 in perfection in summer and autumn. The spiral ar- 

 rangement of its tubes, taken in conjunction with its 

 other characteristics, will enable the young student to 

 distinguish it without much difficulty. 



Polysiphonia subulifera. Awl-bearing Poly- 

 siphonia. 



Fronds tufted, flaccid, from five to eight inches long, about 

 as thick as a bristle; main branches irregularly forked 



