398 = J. C. Draper—Evolution of Structure in Seedlings. 
to the examination of what occurs in the lower forms of veget- 
able organisms found in the air. 
The Fungi, and indeed all plants that are not green, with a 
few exceptions, exhale carbonic acid and never exhale oxygen. 
In this case, in which cell production often occurs with such 
marvelous rapidity, the carbonic acid must have arisen as a 
consequent of the cell growth. It is improbable that it has 
been absorbed by roots and exhaled from the structures, either 
in these plants or in those produced during fermentation. In 
the latter there never are any roots, and in the former, even 
where roots are present, they bear a small proportion to the 
whole plant. The quantity of moisture exhaled by such 
growths is also insignificant, and out of proportion to the car- 
bonic acid evolved. We must, therefore, in this case decline 
to accept the root absorption hypothesis, and admit that the 
carbonic acid has arisen as a result of the cell growth in the 
plant. 
that the evolution of their structures is inseparably attended 
y the formation of carbonic acid, and it seems imposs!D!® 
plant or animal, oxygen and evolve carbonic 4 ‘js 
or some other owidized substance, as an essential condition of the 
evolution of their structures. 
College of the City of New York, Sept. 12th, 1872. 
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