146 Prof. LeConte on the Correlation of Forces. 
“vortex ” of Cuvier is characteristic of animals. There seems no 
reason to believe that a tissue once formed in plants is ever de- 
composed and regenerated, as is the case in animals. When 
plant-cells decompose, the tissue dies. Hence the absolute ne- 
cessity of continuous growth in plants. In this kingdom, life is 
synonymous with growth. There is no possibility of life without 
growth. There is no such thing as determinate size, shape, or 
duration. There is no such thing as maturity; or if so, death 
takes place at the same instant. As cell-life is necessarily of 
short duration, and as there is no regeneration of tissues in 
plants, it is evident that the life of the tissues must be equally 
short. Thus plant-life can only be maintained by the continual 
formation of new tissues and a constant travelling of the vital 
force from the old to the new. In exogenous plants the direec- 
tion of travel is from the interior to the exterior; in endogens 
from exterior to interior, and still more from below upwards, by 
the continual addition of new matter at the apex. In fungi, where 
there is no such superposition of new tissue upon the old, where 
growth takes place by multiplication of cells throughout the 
whole plant—in other words, a true interstitial growth as in 
animals—since there is no regeneration of tissues, the duration 
of the life of the plant is limited by the duration of cell-life. 
The respiration of animals, also, differs essentially from that of 
plants. At one time the absorption of CO® and exhalation of 
O was called the respiration of plants. It is universally admit- 
ted now, however, that this is rather a process of assimilation 
than of respiration. The recomposition and exhalation of CO%, 
as soon as discovered, was very naturally likened to animal re-_ 
spiration, and is in fact looked upon by many, as for example 
the physiologist Carpenter, as a true respiration. But there is 
an essential difference between this and animal respiration, which 
I have already pointed out. Its very significance is radically 
different. The essential object of animal respiration is the re- 
moval of poisonous decomposed matters from the organism. 
The so-called respiration of plants, on the contrary, is rather a 
process of assimilation, since by it the too highly carbonized or- 
ganic food, by the elimination of a portion of its carbon, is 
brought into a proper condition for organization. A true respi- 
ration is necessarily connected with a change of the matter of 
the tissues—with the vortex of Cuvier—which has never been 
shown to exist in plants. It is true the exhalation of CO? has 
been looked upon by some physiologists as indicative of a re- 
generation of tissues; but I have already shown that this is 
probably not the case, but, on the contrary, that the CO? is 
formed by the partial decomposition of highly carbonized or- 
anic food. 
12th. The most natural condition of matter is evidently that of 
