Bauhaus-Universität Weimar

Differences between plants and animals.—Development, 
growth, excitability, propagation, and decay, are the general phe¬ 
nomena and properties of all organised bodies, and are the results 
of organisation; but there are other properties peculiar to animals, 
which may therefore be termed animal in contradistinction to the 
general organic properties. Sensation and voluntary motion 
are the remarkable animal properties. 
Plants, it is true, are not wholly without motion: for their or¬ 
ganisation is attended with internal movements, as in the circulation 
of the sap; their turning spontaneously towards the light, the ex¬ 
tending of their roots in the direction of the most nutritious soil. 
Some plants climb along the surface of bodies which offer them 
means of attachment, and their stamens incline towards the pistil 
at the time of impregnation. Many indeed, particularly those of 
the genus Mimosa, possess in their leafstalks a power of motion 
which can be excited by various irritants, whether mechanical, 
galvanic, or chemical—such as alcohol, mineral acids, æther, and 
ammonia,—as well as by change of temperature or light; thus 
affording another instance of the general law, that the specific ex¬ 
citable properties of organic bodies do not vary in the mode of their 
manifestation according to the nature of the stimulus which ex¬ 
cites them, but are manifested, each in its peculiar manner, on the 
application of the most different stimuli.* In the Hedysarum 
gyrans there is, besides the general influence of light on the motion 
of the larger middle leaflet, an incessant rising and falling of the 
two lateral leaflets, independent of external stimuli; and some of 
the lower vegetables—the Oscillatoria, for example,—present a 
constant vibratory motion. The twining of certain plants is sup¬ 
posed by Palmt to be dependent on their mode of growth causing 
the extremity of the branches to describe circles, and thus enabling 
them to lay hold on near objects; but, however this may be, the 
fact that the Cuscuta twines only around living plants, seems to 
show that, in it, this motion is in some measure dependent on 
organic attraction; and the motions of stamens and leafstalks have 
too much resemblance to the irritability of muscles, not to be com¬ 
pared with it. 
There are then, in plants, organs which, by their movements, re¬ 
semble either tjie muscles or the erectile parts of animals; but there 
is this difference, that the motions of animals are produced not 
merely by the direct action of a stimulus on irritable parts, but 
also by the internal operation of parts not endowed with motion, 
namely, the nerves, on those which have motion. Dutrochet, it is 
true, has observed that, when he directed the focus of a burning- 
* Treviranus, Biologie, v. 201, 229. 
f Palm, über das Winden der Pflanzen, p. 48.


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