172 SPECIFIC HEAT. 



in the depth of winter is the heaviest and fullest of sap." * Warm 

 weather in winter, of too short continuance to afiect the temper 

 ature of the ground sensibly, stimulates a free flow of sap in the 

 maple. Thus, in the last week of December, 1862, and the first 

 week of January, 1863, sugar was made from that tree in various 

 parts of New England. " A single branch of a tree, admitted 

 into a warm room in winter through an aperture in a window, 

 opened its buds and developed its leaves, while the rest of the 

 tree in the external air remained in its winter sleep." f Like facts 

 are matter of every-day observation in graperies where the vine 

 is often planted outside the wall, the stem passing through an 

 aperture into the warm interior. The roots, of course, stand in 

 ground of the ordinary winter temperature, but vegetation is 

 developed in the branches at the pleasure of the gardener. The 

 roots of forest trees in temperate climates remain, for the most 

 part, in a moist soil, of a temperature not much below the annual 

 mean, through the whole winter ; and we can not account for the 

 unintemipted moisture of the tree, unless we suppose that the 

 roots furnish a constant supply of water. 



Atkinson describes a ravine in a valley in Siberia, which was 

 filled with ice to the depth of twenty-five feet. Poplars were 

 growing in this ice, which was thawed to the distance of some 

 inches from the stem. But the surface of the soil beneath it 

 must have remained stiU frozen, for the holes around the trees 

 were full of water resulting from its melting, and this would 

 have escaped below if the ground had been thawed. In this case, 

 although the roots had not thawed the thick covering of earth 

 above them, the trunks must have melted the ice in contact with 

 them. The trees, when observed by Atkinson, were in full leaf, 

 but it does not appear at what period the ice around their stems 

 had melted. 



From these facts, and others of the like sort, it would seem that 

 " aU vegetable functions are " not absolutely " dormant " in winter, 

 and, therefore, that trees may give out some heat even at that 

 season.:}: 



* RossMA-ssLER, Dcr Wald, p. 158. f Ibid., p. 160. 



X All evergreens, even the broad-leaved trees, resist frosts of extraordinary 

 severity better than the deciduous trees of the same climates. Is not this be- 



