steuart's planter's guide. 



259 



ing and the descending sap-vessels : And, secondly, 

 a greater induration of the epidermis, and thick- 

 ness of the cortical layers of the bark are provided ; 

 which, forming a bad conductor of heat, act as a still 

 more effectual defence to the stem, by preventing 

 the immediate and powerful application of cold, 

 through the sudden subtraction of caloric, from the 

 proper vessels of the inner bark. 



" In this economy, nature only follows the ana- 

 logy which she displays in modifying the influence 

 of cold upon the animal kingdom. The quadrupeds, 

 which are destined to encounter the severity of an 

 Arctic winter, are provided with thick and shaggy 

 coats, to enable them to withstand the intensity of 

 the cold ; and all the richest furs, which man em- 

 ploys to supply his natural, or rather his artificial 

 wants, are always furnished by animals inhabiting 

 the highest latitudes, and killed during the severest 

 frosts. What is still more illustrative of the point 

 under consideration is, that the coats of animals, of 

 which the thin and short hair is familiar to us in the 

 temperate climates, such as the dog, the fox, and 

 the ox, are all remarkable, under the polar regions, 

 for their close, lengthened, and almost impenetrable 

 fibre, as a secure barrier of non-conducting matter, 

 to prevent the escape of their vital heat. 



