THE A^JERICAX BOTANIST 



15 



as to climate, shade, moisture and other things as weh. Tem- 

 perature, for instance, plays a large part in the distribution of 

 the green spleenwort (Asplcniuin viridc). It spreads around 

 the world in the Far Xorth, but only occasionally creeps over 

 the northern boundary into the United States. After the 

 maidenhair spleenwort, the little wall rue or rue spleenwort 

 (Asplciiiuiii ruta-inuraria) is probably most often found. It is 

 widely distributed in the Old \\^orld, growing on old walls as 

 well as on rocks, but it never becomes so common with us. 

 Though it ranges from Canada nearly to the Gulf, many ferns 

 students have never seen it growing. 



Still rarer is the mountain spleenwort (Asplaiiiiiii inoyi- 

 taJiuni ) shown in our illustration, which competes with the rue 

 spleenwort in parts of its American range. In general appear- 

 ance it is much like the better known species though its fronds 

 are somew^hat narrower and the pinnules less fan-shaped. In 

 some localities it seems to be a fairly common species, but in 

 many large areas it is marked rare or absent. Like many of 

 its congeners, it roots in crannies so narrow that it can only be 

 dug out with difficulty if at all, and it is probable that this 

 habit, together with its small size has had much to do with 

 preserving it from extinction. Its preference is for rather 

 dryish rocks and it can endure some sunshine though it flour- 

 ishes best in shade. 



