138 BRITISH SEA-WEEDS. 



consisting of a primary leaf two to eight inches in length, 

 tapering at each end, with a strong midrib, and indistinct 

 transverse veins ; numerous smaller leaves spring from the 

 midrib, and in their turn produce others, until the plant 

 becomes very bushy. Spores very minute, in globose con- 

 ceptacles formed in the substance of the midrib ; tetra- 

 spores in linear sori, on each side of the midrib of the 

 small leaves. 



This plant is less common on our shores than either 

 D. sinuosa or D. alata, and English specimens are gene- 

 rally small and stunted. On the west coast of Ireland, 

 especially at Bantry Bay, it grows in great abundance, 

 and is of a very large size, frequently attaining a height 

 of eight or nine inches. It is also of a brighter colour, 

 and more delicate texture, but even here small specimens 

 occasionally occur among their more luxuriant bre- 

 thren. This is a summer species, and annual. 



Delesseria ruscifolia. The obtuse-leaved 

 Delesseria. 



Fronds from two to four inches high, growing in tufts ; 

 primary leaves linear-oblong, undivided, blunt at the tip, 

 often somewhat waved and curled, having a strong midrib, 

 from which springs a secondary series of smaller leaves, 

 which again from their midribs produce a third series 

 in the same manner, and so on ; all the leaves are similar; 

 the membrane of which they are formed is composed of 

 minute, densely-packed, angular cellules, and is traversed 

 by anastomosing, branched, jointed veinlets, which run 

 obliquely from the midrib to tlie margin of the leaf. 

 Spores in conceptacles seated on tlie midrib, generally near 

 the tips of the younger leaves ; tetraspores in linear sori, 

 disposed on each side of the midrib. 



