158 
SPECIFIC TEMPERATURE OF TREES. 
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 observed; but it is inconsistent with general prin¬ 
ciples that heat should be generated where no change is 
taking place.” 
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, 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 u 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 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 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 
* Rossmassler, Der Wald , p. 158. 
t Ibid., p. 160. 
