MOVEMENTS OF PLANTS. 859 
good green colour ; but those exposed to the electric light for six 
hours per day only, being in darkness the other eighteen hours, 
were vigorous though less green ; while those exposed to day- 
hght and electric light successively, were the most vigorous, and 
the green of their leaves of a darker hue. This shows that 
plants may for a time grow continuously without rest, i.e. with- 
out sleep ; but for what length of time this endurance would 
continue further experiments are required to prove. The 
electric light seems therefore to affect plants in a similar manner 
to the continuous summer sun in northern latitudes, where 
Dr. Schiibeler found that the arctic sun caused plants to pro- 
duce more brilliant flowers and richer and larger fruit than if 
the same plants had been grown with an alternation of light 
and darkness. 
4. Movements or Piants.—Three kinds of movements have 
been described in plants :—1. Motions of entire plants, such as 
those which occur in the Oscillatorieze, Diatomezx, and some 
other forms of the lower Algz ; and of parts, e.g. the anthero- 
zoids, connected with the reproductive processes in some of the 
lower kinds of plants. The movements thus possessed by 
some of the lower Algz is a marked deviation from what ord1- 
narily occurs in plants. 2. Movements produced in parts of 
plants which are dead, or which. at least, have lost their active 
vitality. Such movements may be noticed in almosi all the 
great divisions of plants, and are more or less connected with 
some reproductive function. We include here the bursting of 
anthers in the Phanerogams, and that of spore-cases in the 
Cryptogams the dehiscence of fruits, the separation of the 
component carpels from one another in the Euphorbiacezw and 
Geraniaceze, and many other phenomena of a like nature. 3. 
Movements which occur in the living parts of plants when in an 
active state of growth, &c. 
The first two classes of movements have been already alluded 
to in various parts of this work. The movements of the first 
class appear to depend upon a rotation of the protoplasmic cell- 
contents, the cause of which is at present unexplained ; or to 
the presence of cilia upon their surfaces. Movements of the 
second kind are entirely mechanical, and produced by the vary- 
ing conditions of the different tissues as to elasticity and power 
of imbibing moisture. 
The third kind of movements must be more particularly 
noticed. They only occur during active vegetation. The 
directions taken by organs properly come under this head. But 
this matter, so far as the plumule and radicle are concerned, 
has been already noticed (page 854). With regard to the stem 
the extensive researches of Darwin on Twining Plants and 
Tendrils are full of interest. The ends of such structures have 
the power of spontaneously revolving ; and this they constantly 
do, usually from right to left, once in about two hours ; to this 
