



212 THE BRITISH FERNS. 
fascicle bears a sorus, but occasionally on the lowest pinnules the 
posterior basal venule also is fertile. The veins are conspicuously 
depressed on the upper surface. 
Fructification on the back of the fronds, usually confined to the 
upper half, but sometimes extending lower down. Sori numerous, 
round, indusiate, medial on the anterior basal venules, in a row on 
each side of and nearer to the midrib than the margin, except in 
the most luxuriant pinnules, where the development of sori on the 
posterior venules produces a more irregular arrangement. Indu- 
sium membranaceous, reniform, flat, with a wavy, somewhat irregular 
margin, but without glands, affixed by a deep basal sinus.  Spore- 
cases numerous, dark brown, roundish. Spores oblong, granulated. 
Duration. The caudex is perennial. The fronds are annual, the 
earliest being produced in May, and these are succeeded by others 
during the summer, all becoming destroyed by the autumnal frosts, 
or perishing even if not exposed. 
Lastrea cristata, with the plants called uliginosa and spinulosa, 
form a group distinguishable by habit and other characters from 
the allied dilatata group, with which, however, the more highly 
developed form, spinulosa, is sometimes associated by botanists of 
high authority—in consequence, no doubt, of the plants having 
been studied in the herbarium, where their differences become 
less marked, rather than in a state of growth, in which certain impor- 
tant characters are obvious. Of this first-mentioned group, Lastrea 
cristata is the least developed form. In our Handbook of British Ferns 
(2 ed.) it was treated as consisting of three forms of one not very 
variable species ; and notwithstanding that many Fern authorities do 
not appear to adopt this view, we have no doubt whatever that the 
plants possess a close natural affinity, and have characters which 
separate them from the forms of Lastrea dilatata, however similar to 
the latter, in some cases, may be the degree and mode of division in 
the fronds—points on which botanists are at times too prone to rely. 
The close affinity of the three forms now alluded to, is evidenced by 
marks far more important than those to be derived from such 
characters as the outline or cutting of the fronds: namely, by the 
creeping caudex, by the erect narrow fronds, by the sparse and 

