140 THE WOOD FERNS. 
nules which are crenulate or finely serrate. Occasionally 
the pinnules nearest the rachis are separate. Fertile 
fronds sometimes reach a height of three feet and a width 
of six inches, but these dimensions are rare. The sori 
are borne in a double row on each pinnule and the in- 
dusium is broad, thin and conspicuous. A fruiting pin- 
nule is illustrated in the Key to the Genera. The 
rootstock is of medium size, horizontal and creeping. 
Aspidium cristatum, Middle pinnas. 
The crosiers are covered with broad, light-brown scales, 
many of which remain on the stipes after the blade has 
unfurled. 
This species is very sensitive to varying amounts of 
light and the pinne, especially those of the fertile frond, 
have the trick of assuming a nearly horizontal position 
like slats in a blind, to accommodate themselves to the 
illumination. In fronds that do not naturally receive 
sufficient light, the individual pinne will twist around 
until at the proper angle. Even when a frond is fastened 
with the upper side down, they will manage to turn so 
as to face the light. 
The crested fern is found from northern Canada to 
North Carolina, Arkansas and Idaho and occurs again in 
Europeand Asia. Its favourite haunt is the woodland 
