J. LeConte on the Correlation of Forces. sty 
llth. In what then consists the essential difference between 
animals and plants? There can be no doubt that it consists, 
generally, in their relations to one another and to the mineral 
ingdom. Plants occupy a middle ground between the mineral 
and animal kingdom—a necessary halting place for matter in its 
upward struggles. But when we attempt to define this relation 
more accurately, the problem becomes much more difficult. It 
is indeed probable that no single distinction will be found free 
from objection. The commonly received and, toa certain ex- 
tent, very correct idea is, that the essential distinction consists in 
their relation to CO,. Plants decompose and animals recom- 
pose CO,. The beautiful manner in which the two kingdoms 
stand related to each other through these converse processes, is 
familiar to all. But it is well known that most plants carry on 
both of these processes at the same time, while some, as fungi, 
pale plants, &., only recompose CO, like animals. It seems to 
me that at least an equally good fundamental distinction may be 
found in this, that in plants the fundamental and necessary 
source of vital force is the decomposition of its mineral food ; 
while in animals the fundamental source of vital force is the de- 
composition of its tissues. It is true that in what I have called 
; but 
erence, that in plants this de- 
composition of organic food is only partial, and therefore fur- 
nishes not only force but material for organization ; while in 
animals the decomposition is complete and therefore furnishes 
only force, 
