ATHYRIUM. 
125 
selves. The hippocrepiform sorus is formed by the lateral 
line of spore-cases crossing the vein and returning on the 
opposite side ; sometimes in the case of the curved, or 
horseshoe-shaped sori, the indusium is apparently almost 
circular, with a lateral notch, and in this state the 
fructification somewhat resembles that of Lastrea. One 
side of the indusium is fixed longitudinally to the side of 
the vein which forms the receptacle ; its other margin, the 
anterior one, or that towards the midvein of the pinnule, 
becomes free, and is fringed, or split into a number of 
hair-like segments. This description applies to the com- 
moner forms of the Lady Fern ; but even these are very 
variable in size, according to the situation and circum- 
stances which influence their development, sometimes 
scarcely exceeding a foot in height, and at other times 
reaching the height of four or five feet, the latter being 
the result of growth in a damp, shady situation, the former 
the consequence of a more exposed and drier locality. 
The variety rhseticum, sometimes called comexum^ 
difiers from the forms already described in its more lady- 
like proportions, both its fronds, its pinnae, and its 
pinnules being often smaller and usually more slender and 
narrower, or narrower-looking, than in them. The fronds 
