THE BRITISH FERNS. 


Genus VI: ATHYRIUM, Roth. 
GEN. Cuar.—Sori indusiate; short oblong-lunate, hamate, or the 
basal ones more or less equally hippocrepiform ; the receptacles 
occupying the anterior side, sometimes crossing and returning 
along the posterior side of the veins. Indusium of the same form, 
often lacerate-fimbriate at length reflexed by the crowded spore- 
cases. Veins simple or forked from a central costa; venules free, 
sometimes pinnate. 
Fronds herbaceous bi-tri-pinnate, having the sori more or less 
generally (the basal ones usually, rarely nearly all) arcuate. 
Caudex short, erect or creeping. 
This genus holds as it were a middle place between the Aspidice, 
which have punctiform sori, and the Aspleniew, in which they are 
linear. It belongs indeed to the latter group, the greater part of 
the sori being elongated, and a considerable proportion of them quite 
asplenioid ; but others of them clearly indicate a passage from the 
straight elongate form typical of Asplenium, to the short reniform 
condition characteristic of Lastrea. The first indication of this 
change is seen in the curving of the upper ends-of certain of the sori 
near the base of the pinnules, which eurving produces what has been 
called a hamate or hooked form of sorus. This hooked condition of 
the sorus is farther changed in the anterior basal sori of most of the 
‘more divided forms of the common Lady Fern, to that of an equal- 
sided curve, resembling the figure of a horseshoe. Such equally- 
curved sori come very near indeed to those of Lastrea, and there can 
VOL. II. . B 

