BRITISH FERNS. 



77 



The root of A. marinum is black, wiry, tough, long, and so 

 firmly fixed in the crevices of rock that it cannot be eradicated 

 without the greatest difficulty : the rhizoma is nearly spherical, 

 black, and covered with bristly scales : the fronds make their 

 appearance in June and July, ripen their seed in October, and 

 remain green throughout the year : in July and August fronds 

 of successive seasons may be found equally vigorous. 



The frond is linear, and simply pinnate : the pinnae are stalked, 

 ovate, and serrated ; two larger ones frequently occur near the 

 apex : the pinnae are connected by a narrow wing running along 

 the rachis, as shewn in the figure of the Cornish plant in the 

 preceding page, the upper left hand figure representing a portion 

 of the rachis. 



The lateral veins are forked almost immediately after leaving 

 the midvein ; the anterior branch bears an elongate linear mass 

 of rust-coloured thecae, which, when young, is covered by a 

 white membranous indusium of the same shape as the mass, and 

 always opening towards the apex of the frond. 



Adiantum trapeziforme of Hudson, Bolton, Berkenhout, &c. 

 I believe to be nothing more than the Cornish form of this 

 species. 



