Part III.] OR POISONED BY VEGETABLE GROWTH? 
207 
Now, to prevent the effect of my aerial denuda¬ 
tion, let us bury the heads as well as the roots 
of these plants below the soil. Every such 
plant, large or small, will, in decay, become a 
hoard of carbonic acid fixed in the soil for the 
good of future plants, in addition to the annual 
supply of carbonic acid and ammonia to the soil 
from the air and from rain. The carbonic acid 
of decaying vegetation will also help the rain in 
disintegrating our powdered rock. So that ve¬ 
getation may be said to produce vegetation; 
and we may possibly see in this general tendency 
to the increase of vegetable remains a main cause 
of the formation of bogs: and perhaps aqueous 
denudation may be a necessary agent to prevent 
the undue increase of vegetable remains over 
the whole surface of the earth. 
And natural forests return to the soil all they 
take from it, and with interest; and Lyell 
should not talk of trees dying out from the soil 
having “ become exhausted for trees,” or of the 
necessity of rotation in nature’s cropping. No¬ 
tation of crops is only necessary where man robs 
the soil of the produce he has raised, or raises 
plants by cultivation such as nature could not 
raise without cultivation. 
It is perhaps probable that were wheat sown 
No necessity 
for rotation in 
nature’s crop¬ 
ping. 
