SPECIFIC HEAT. 171 



highest ; but if the temperature of the air rises to 18°, that of 

 the vegetable growth is the lowest. Since, then, trees maintain 

 ^t all seasons a constant mean temperature of 12° [= 54° Fahr.], 

 it is easy to see why the air in contact with the forest must be 

 warmer in winter, cooler in summer, than in situations where it 

 is deprived of that influence." * 



Professor Henry says : " As a general deduction from chemical 

 and mechanical principles, we think no change of temperature is 

 ever produced where the actions belonging to one or both of 

 these principles are not present. Hence, in midwinter, when all 

 vegetable functions are dormant, we do not believe that any heat 

 is developed by a tree, or thafits interior differs in temperature 

 from its exterior further than it is protected from the external 

 air. The experiments which have been made on this point, we 

 think, have been directed by a false analogy. During the active 

 circulation of the sap and the production of new tissue, variations 

 of temperature belonging exclusively to the plant may be ob- 

 served ; but it is inconsistent with general principles that heat 

 should be generated where no change is taking place." f 



There can be no doubt that moisture is given out by trees and 

 evaporated in extremely cold winter weather, and unless new fluid 

 were supplied from the roots by the exercise of some vital func- 

 tion, the tree would be exhausted of its juices before winter was 

 over. But this is not observed to be the fact, and, though the 

 point is disputed, respectable authorities declare that " wood felled 



* Memoria sur BoscM della Lombardia, p. 45. 



The results of recent experiments by Becquerel do not accord with those 

 obtained by Meguscher, and the former eminent physicist holds that " a tree 

 is warmed in the air like any inert body." At the same time he asserts, as a 

 fact well ascertained by experiment, that " vegetables possess in themselves 

 the power of resisting extreme cold for a certain length of time, .... and 

 hence it is believed that there may exist in the organism of plants, a force, 

 independent of the conduction of caloric, which resists a degree of cold above 

 the freezing-point." In a following page he cites observations made by 

 Bugeaud, under the parallel of 58° N. L., between the months of November 

 and June, during most of which time, of course, vegetable life was in its 

 deepest lethargy. Bugeaud found that when the temperature of the air was 

 at — 34°. 60, that of a poplar was only at — 29°. 70, which certainly confirms 

 the doctrine that trees exercise a certain internal resistance against cold. 



t United States Patent Office Report for 1857, p. 504. 



