66 
COURSE OF THE SAP. 
[Part II. 
climates, where a sky seldom clouded permits 
the glowing rays of the sun to shine upon an 
immeasurably luxuriant vegetation. The tem¬ 
perate and cold zones, where artificial warmth 
must replace deficient heat of the sun, produce, 
on the contrary, carbonic acid in superabundance, 
which is expended in the nutrition of the tropical 
plants. The same stream of air which moves by 
the revolution of the earth from the equator to 
the poles brings to us, in its passage from the 
equator, the oxygen generated there, and carries 
away the carbonic acid formed during our winter.” 
Now, in reference to “ the temperate and cold 
zones,” it appears to me a contradiction to say 
that the carbon of all our plants is formed from 
the carbonic acid in the air, and that the super¬ 
abundance of carbonic acid in the air is formed 
by the plants. And in reference to u the tropics 
and warm climates,” suppose this soldier’s* wind 
to have conveyed the two gases to their opposite 
destinations, tropical heat generates aridity and 
sterility, unless where the soil is irrigated by 
nature or art. What farther proof can we want 
* But perhaps Liebig will lay a down-line to the tropics 
above his up-line to the poles. And will he dispatch his 
luggage-trains of heavy carbonic acid gas by that ? Gravity 
forbid!! 
