SPECIFIC HEAT. Ve 
mant” in winter, and, therefore, that trees may give out some 
heat even at that season.” 
It does not appear that observations have been made on the 
special point of the development of heat in forest trees during 
florification, or at any other period of intense vital action; and 
hence an important element in the argument remains undeter- 
mined. The “circulation of the sap” commences at a very 
early period in the spring, and the temperature of the air in 
contact with trees may then be suficiently affected by heat 
* All evergreens, even the broad-leaved trees, resist frosts of extraordinary 
severity better than the deciduous trees of the same climates. Is not this 
because the vital processes of trees of persistent foliage are less interrupted 
during winter than those of trees which annually shed their leaves, and that 
therefore more organic heat is developed ? 
In crossing Mont Cenis in October, 1869, when the leaves of the larches on 
the northern slope and near the top of the mountain were entirely dead and 
turned brown, I observed that these trees were completcly white with hoar- 
frost. It was a wonderful sight to see how every leaf was covered with a 
delicate deposit of frozen aqueous vapor, which gave the effect of the most 
brilliant silver. On the other hand, the evergreen coniferze, which were grow- 
ing among the larches, and therefore in the same conditions of exposure, were 
almost entirely free from frost. The contrast between the verdure of the 
leaves of the evergreens and the crystalline splendor of those of the larches 
was strikingly beautiful. Was this fact due to a difference in the color and 
structure of the leaves, or rather is it a proof of a vital force of resistance to 
cold in the living foliage of the evergreen tree ? 
The low temperature of air and soil at which, in the frigid zone, as well as 
in warmer latitudes under special circumstances, the processes of vegetution go 
on, seems to necessitate the supposition that all the manifestations of vegeta- 
ble life are attended with an evolution of heat. In the United States it is 
common to protect ice, in ice-houses, by a covering of straw, which naturally 
sometimes contains kernels of grain. These often sprout, and even throw out 
roots and leaves to a considerable length, in a temperature very little above 
the freezing-point. Three or four years since I saw a lump of very clear and 
apparently solid ice, about eight inches long by six thick, on which a kernel of 
grain had sprouted in an ice-house, and sent half a dozen or more very slender 
roots into the pores of the ice and through the whole length of the lump. The 
young plant must have thrown out aconsiderable quantity of heat; for though 
the ice was, as I haye said, otherwise solid, the pores through which the roots 
passed were enlarged to perhaps double the diameter of the fibres, but still 
not so much as to prevent the retention of water in them by capillary attrac- 
tion. 
