THE planter's guide. 



65 



temperature, vegetation is positively promoted. Below 

 or above a certain point, (the degree differing in different 

 species of plants,) vegetation is positively checked. To 

 speak only of the latter case, which is briefly expressed by 

 the term cold, it is either produced by absolute lowness 

 of temperature, or, in particular circumstances, by the 

 generation of cold, through the effect of wind, and con- 

 sequent evaporation from a moist surface; for trees in 

 themselves have but little self-generated heat above the 

 surrounding temperature; and their chemical composition 

 is such that they do not congeal, unless the cold be of 

 the severest sort, and many degrees below the freezing 

 point of water. Some caloric, however, they probably 

 possess, otherwise they would be killed in very hard 

 weather, or rather on the too sudden return of heat.''^ 



Of the above accidents nature can modify the former, 

 by accommodating different species of plants to different 

 latitudes and elevations. Against the latter, she adopts 

 the plan of affording suitable protection to the individual. 

 In the interior of woods, where the free current of air is 

 intercepted, where stillness and serenity are maintained, 

 j and where each tree affords shelter more or less to every 

 I other, nature has little need to generate the provisions 

 necessary to mitigate the injurious effects of evaporation. 

 I But in open exposures, and in the case of isolated trees, 

 1 this effect must be assuaged, and is in fact to a certain 

 I extent alleviated, by various provisions or properties 

 bestowed upon the tree itself In the first place, a 

 thicker and closer ramification of the sides and top is 

 i supplied, and a more abundant spray towards the stormy 

 i quarter, thereby famishing a kind of clothing of leaves, 

 in order to protect from cold both the ascending and the 



* Note IV. 



E 



