n INTEGUMENTARY VARIATIONS 91 



daily per 1,000 kilograms of sheep varies in the 

 following proportions according to the food : 



Kg. 



o'69i of wool : scanty winter food. 

 0*870 ,, plenty of hay. 



0*958 ,, good pasture. 



ro8o 1*240 ,, fattening process. 



If we now turn to plants, we perceive the same 

 variability in the superficial integumentary organs. 

 I merely recall here because I shall have to refer to 

 it at greater length later on the considerable differ- 

 ences which many observers have recently noticed in 

 the anatomy and characters of the same parts which 

 successively lead aquatic and aerial lives. In these 

 cases the influence of environment is easily to be 

 traced and appreciated. It is also well known that 

 where mountain-plants are transferred to the valleys 

 and plains they lose the hairy covering which they 

 generally possess, while valley-plants transferred to 

 the mountains acquire this same covering. Linnaeus 

 noticed that Persicaria is devoid of this sort of down 

 when living in humid places, while it becomes very 

 villous in dry stations. The same is noticed of 

 Thymus serpyllum. Many plants, in short, exhibit 

 two varieties which are readily distinguishable the 

 glabrous and the villous ; such are Prismatocarpus 

 speculum, Isatis tinctoria, Jasione montana, Onopordon 

 acanthium. 



