MOVEMENTS OF PLANTS. 805 



been made upon tlie electrical condition of plants are vague 

 and unsatisfactory. It is said by some that electricity is deve- 

 loped during the ordinary growth of plants, as in germination 

 and exhalation. Plants are also stated to be commonly in a 

 negative condition as regards their electricity, but that different 

 parts of plants may exhibit opposite electrical phenomena. 



4. Movements of Plants. — Three kinds of movements have 

 been described in plants: — 1. Motions of entire plants, such as 

 those which occur in the Oscillatorit-ge, Diatomacese, and some 

 other forms of the lower Algae ; and of parts, e. g. the sperma- 

 tozoids, connected with the reproductive processes in some of the 

 lower kinds of plants. The locomotive power thus possessed by 

 some of the lower Algse is a marked deviation from what ordi- 

 narily occurs in vegetables. 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 almost 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 higher classes of plants, and that of spore-cases 

 in the lower; the dehiscence of fruits, the separation of the 

 component carpels from each other in the Euphorbiacese and 

 Geraniaceae, 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 cilise upon their surfaces. Movements of 

 the second kind are entirely mechanical, and produced by the 

 varying conditions of the different tissues as to elasticity and 

 power of imbibing moisture. 



The third kind of moA-ements must be more particularly 

 notice.!. They only occur during active vegetation. The 

 directions taken by organs properly come iinder this head. 

 This matter, so far as the Plumule and Radicle are concerned, 

 has been already noticed (p. 788). "With regard to the stem the 

 recent extensive researches of Mr. Darwin on Twining plants 

 and Tendrils are full of interest. The ends of such organs have 

 the power of spontaneously revolving; and this tliey constantly 

 do, usually from right to left, once in about two hours. As soon 

 as the organ meets with a support its motion is arrested and it 

 becomes spirally twined round by the arrest of the movement 

 of successive portions. Tendrils contract spirally soon after 

 they have laid hold of a support, and so draw up the stem to 

 which they are attached. The remaining movements belonging 

 to this class have been divided by Schleiden in the following 



