398 The Movements of Plants 
Darwin’s view is plainly stated on pp. 3—4 of the Power of 
Movement. Speaking of circumnutation he says, “In this universally 
present movement we have the basis or groundwork for the acquire- 
ment, according to the requirements of the plant, of the most 
diversified movements.” He then points out that curvatures such 
as those towards the light or towards the centre of the earth 
can be shown to be exaggerations of circumnutation in the given 
directions. He finally points out that the difficulty of conceiving 
how the capacities of bending in definite directions were acquired 
is diminished by his conception. “We know that there is always 
movement in progress, and its amplitude, or direction, or both, have 
only to be modified for the good of the plant in relation with internal 
or external] stimuli.” 
It may at once be allowed that the view here given has not been 
accepted by physiologists. The bare fact that circumnutation is a 
general property of plants (other than climbing species) is not 
generally rejected. But the botanical world is no nearer to be- 
lieving in the theory of reaction built on it. 
If we compare the movements of plants with those of the lower 
animals we find a certain resemblance between the two. Accord- 
ing to Jennings! a Paramecium constantly tends to swerve towards 
the aboral side of its body owing to certain peculiarities in the set 
and power of its cilia. But the tendency to swim in a circle, thus 
produced, is neutralised by the rotation of the creature about its 
longitudinal axis. Thus the direction of the swerves in relation to 
the path of the organism is always changing, with the result that the 
creature moves in what approximates to a straight line, being how- 
ever actually a spiral about the general line of progress. This 
method of motion is strikingly like the circumnutation of a plant, 
the apex of which also describes a spiral about the general line of 
growth. A rooted plant obviously cannot rotate on its axis, but the 
regular series of curvatures of which its growth consists correspond 
to the aberrations of Paramecium distributed regularly about its 
course by means of rotation. Just as a plant changes its direction 
of growth by an exaggeration of one of the curvature-elements of 
which circumnutation consists, so does a Paramecium change its 
course by the accentuation of one of the deviations of which its 
path is built. Jennings has shown that the infusoria, etc., react to 
stimuli by what is known as the “method of trial.” If an organism 
1H. 8. Jennings, The Behavior of the Lower Animals. Columbia U. Press, N.Y. 
1906. 
* In my address to the Biological Section of the British Association at Cardiff (1891) I 
have attempted to show the connection between circumnutation and rectipetality, i.e. the 
innate capacity of growing in a straight line. 
