24:0 COMPARISON BETWEEN ANIMALS AND PLANTS. 
history, to say which is called animal and which vegetable 
Wq have seen among the zoophytes, that the polypus, like a 
vegetable, may be increased by cutting shoots and ingrafting 
them upon other animals. With respect to sensation, some 
plants seem to possess this, apparently even in a greater degree 
than some of the last orders of animals : — the sensitive-plant 
shrinks from the touch ; the Dionea suddenly closes its leaves 
upon the insect which touches them ; the leaves of plants fol- 
low the direction of light in order to present their upper sur- 
faces to its influence, as may be observed in flower-pots placed 
in a window. The seed of a plant in whatever situation it 
may be placed in the earth, always sends its root downward 
and its stem upward ; in these cases, does there not seem as 
much appearance of sensation and instinct, and even more, 
than in the lower orders of animals ? 
383. We find, then, that the possession^ or want of instinct, 
does not constiimte a mark of distinction between animals and 
plants. 
Some have attempted to draw a line of distinction, by con- 
sidering that locomotion, or the power of changing place,helongs 
to animals only ; but this criterion seems to fai'l, since we find 
animals fixed to the hottom of tlie sea, or growing upon rocks, 
and plants moving upon the surface of the water. 
Another mark of distinction has been given, in the supposed 
^presence of nitrogen in animals, detected by a peculiai odor 
when animal substances are burning, similar to what we per- 
ceive in the combustion of bones ; but nitrogen having heen 
discovered in some vegetables, this proof is no longer considered 
infallible. 
384. It appears, then, from a comparison between animals 
and vegetables, that these beings are closely connected by the es- 
sential characters of organization / that it is impossible to dis- 
tinguish them by any trait that belongs exclusively to either : 
that the connection between them appea/rs the most striking in the 
least perfect species of both kingdoms; and that, as we recede 
from this point, the differences become more numerous and 
more marked. We may illustrate this view by imagining two 
ascending chains rising from one common point, each side of 
the chain becoming more and more unlike in proportion to the 
intervening distance from the center. From this same, wntral 
point also proceeds the chain of inorganized sid)stances / — sonvC 
imperfect animals resembling plants in their outward form} 
some, both of animals a/nd plants, resembling minerals in theit 
ha/rd and calcareous coverings and shapeless forms. 
Sra. Dwtiiiction between animals and plante.— 364. Resemblance*. 
