Q48 PRINCIPLES OF BOTANY, ETC. 
portion to the different thickness of the stem. He 
made some other experiments by means of a ther-. 
mometer, comparing the temperature of the atmo- 
sphere with that of the leaves. ‘The above related 
experiments of Mr Hunter plainly shew, that the 
juices of plants have a peculiar temperature of their 
own. But those of Schoepf cannot serve, as he 
himself acknowledges, as decisive prdofs, because 
the ligneous stems of plants possess a less degree of 
vital power, and indeed the inner bark only (as we 
shall soon have occasion to observe, § 297), 1s m 
every tree or shrub the seat of this power. The 
power of conducting caloric, which certainly in 
wood is not so strong as in other bodies, alone, pro- 
duces a change of temperature, and renders the ex- 
periments of Mr Schoepf very uncertain*. 
bet 
S45 Alon 
But the consideration of the different powers.of 
vegetables, their chemical component parts, the 
structure of their vessels, of the process of absorp- 
tion, of exhalation and temperature, is not sufficient 
to convey a complete idea of a plant, We shall, 
therefore, go through the whole vegetable world, 
oy 
* Grass, froots, and the pine tribe, and all plants in gene- 
ral which have a more tenacious sap, and can resist.cold better 
than others. But trees which lose their leaves, are, as long as the 
leaves remain, very' susceptible of its impression. ‘Tvhe reason 
seems to be, that all sap, as long as the stem has its leaves, 
circulates very quickly, and being thimner, is more liable to 
suffer by cold. We find, in early winters, that those trees 
which lose their leaves, do not suffer in the least by cold. 
from 
