174 SPECIFIC HEAT. 
fact, and, though the point is disputed, respectable authorities 
declare that “wood felled in the depth of winter is the heaviest 
and fullest of sap.”* Warm weather in winter, of too short 
continuance to affect the temperature 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 Eng- 
land. “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 exter- 
nal air remained in its winter sleep.”+ 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 cannot account for 
the uninterrupted 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 still 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 con- 
tact 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 “all vegetable functions are” not absolutely “ dor- 
* RossMissLer, Der Wald, p. 158. } Ibid., p. 160. 
