258 



NOTICES OF AUTHaRS. 



Cold, it is either produced by absolute lowness of 

 temperature, or, in particular circumstances, by the 

 generation of cold, through the eifect of wind, and 

 consequent evaporation from a moist surface ; for 

 trees, in themselves, have but little self-generated 

 heat, above the surrounding temperatui'e. Some 

 they certainly possess, otherwise they would be killed 

 during severe frosts. Of the above accidents nature 

 can modify the former, by accommodating different 

 species of plants to different latitudes and eleva- 

 tions : Against the latter she adopts the plan of af-- 

 fording suitable protection to the individual. In 

 the interior of woods, where the free current of air 

 is intercepted, where stillness and serenity are main- 

 tained, and where each tree affords shelter, more or 

 less, to every other, nature has little need to gene- 

 rate the provisions necessary to mitigate the injuri- 

 ous effects of evaporation. But, in open exposures, 

 and in the case of isolated trees, this effect must 

 be assuaged, and is, in fact, to a certain extent alle- 

 viated, 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 sup- 

 plied, and a more abundant spray towards the stor- 

 my quarter, thereby furnishing a kind of clothing of 

 leaves, in order to protect from cold both the ascend- 



