MOVEMENTS OF PLANTS. 789 



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. MOVE3IENTS OF PLANTS. — Three kinds of movements 

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

 such as those which occur in the Oscillatoriese, Diatomacese, 

 and some other forms of the lower Algae; and of parts connected 

 with the reproductive processes in some of the lower kinds of 

 plants. The locomotive power thus possessed by some of the 

 lower Algae is a marked deviation from what ordinarily occurs 

 in vegetables. 2. Movements produced in parts of plants which 

 are dead, or which, at least, have lost their active vitality. 

 Such movements maybe 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 Euphorbiaceae and Geraniaceae, and 

 many other phenomena of a hke 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 

 varying 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. 

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

 has been already noticed (p. 771). We shall not further allude 

 to this portion of the subject. The remaining movements 

 belonging to this class have been divided by Schleiden as 

 follows : — 



1. Movements which evidently depend on external influences. 



These are again divided into two: — 

 a. Periodical. 

 6. Not periodicaL 



2. Movements independent, at least to some extent, of ex- 



ternal influences, which are also divided into two : — 



a. PeriodicaL 



b. Not periodical. 



1. Movements depending on external Influences — a. 

 Periodical. — Under this head we include such movements as 

 3e4 



