LAURENCIACE^. 121 



from two to six inches high ; branches alternate, or rarely 

 opposite ; branchlets crowded, tapering at the base, truncated 

 at the tips. Spores not hitherto observed ; tetraspores tri- 

 partite, numerous, imbedded in the substance of the frond 

 at the tips of the branchlets. 



This plant was formerly considered to be only a variety 

 of L. pinnatifida, and Dr. Harvey, in his 'Phycologia/ 

 offers it as a species " with some hesitation." It is, with- 

 out doubt, an instance of the difiBculty of determining 

 the species of this genus to which I have already alluded ; 

 but while I admit that it is not easy to distinguish be- 

 tween L. ctBspitosa and certain states of L. pinnatifida, 

 and even of L. obtusa in dried specimens, I must add 

 that I have always found the general characters of grow- 

 ing or fresh plants sufficiently distinct. L. caaspitosa has a 

 cylindrical form and a pyramidal, bushy habit of growth ; 

 its fronds are soft and gelatinous, and, in consequence, 

 adhere closely to paper. L. pinnatifida, on the other 

 hand, has throughout, a flat spreading habit ; its fronds 

 are of a hard, close texture, and cartilaginous and, there- 

 fore, much less adhesive when dry. L. obtusa has oppo- 

 site branches, is of a brighter red colour, and differs 

 generally in appearance from this species. L. ccespiiosa 

 is annual, and grows on stones between the tide-marks. 

 It is common all round our coasts. 



Laurencia obtusa. Obtuse Laurencia. 



Fronds cylindrical, threadlike, twice or thrice pinnate, 

 from two to nine inches long, growing in large tufts ; 

 branches opposite, spreading ; branchlets short, spreading, 

 club-shaped, blunt at the tip. Spores in egg-shaped, fre- 

 quently imperfect, conceptacles, at the tips of the branchlets ; 



