66 



THE planter's GUIDE. 



descending sap-vessels : and secondly, a greater indura- 

 tion of the epidermis, and thickness 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, natm-e only follows the analogy 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 employs to supply his natural, or rather his artificial 

 wants, are always furnished by animals inhabiting the 

 highest latitudes, and killed duiing the severest frosts. 

 What is still more illustrative of the point under consider- 

 ation 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.''^ 



In like manner, in all the other relations, we see nature 

 especially accommodating the character of each individual 

 plant to the exigencies of its particular situation. In the 

 interior of woods, the wind can exert a far less mechanical 

 efi*ect on individual trees ; and therefore, while they are 

 positively determined to push upwards towards the light, 

 they are negatively permitted to do so by the removal of 

 any necessity to thicken their trunks, for the sake of 

 greater strength, and to contract the height of them, in 



* Note V. 



