156 JOHN MACOUN ON CANADIAN POLYPETALZÆ, 
species unaided can never pass from a southern station to a northern one without a very 
great increase of temperature. It is not my purpose to discuss the origin of types but, these 
once established, I can see no difficulty in the way of variation through the very exuber- 
ance of their innate powers. No one who has studied the multiplicity of forms in one of 
our large genera can doubt the close relationship which exists between certain groups of 
species and we are led to doubt the power of words to limit them. 

