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 pinnae. 



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 pinnae, 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 pinnae 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 

 Europe and Asia. Its favourite haunt is the woodland 



