296 LECTURE XIV. 



which do not affect destructive metabolism at all. We have 

 just learned, for instance, that growth is restricted to nar- 

 rower limits of temperature than is destructive metabolism. 

 Again, we saw, in the last lecture (p. 261), that light does 

 not materially affect destructive metabolism as estimated by 

 respiration : but, as we shall learn in a subsequent lecture 

 when we are studying the mechanics of growth, light has a 

 remarkable effect upon growth. 



Movement. Without entering for the present into the 

 mechanics of the movements exhibited by plants, we will 

 consider those facts relating to movement which prove that 

 it is dependent upon destructive metabolism and that it in- 

 volves a loss of energy to the plant. We may, however, 

 briefly enumerate the different ways in which movement 

 manifests itself. The lowest expression of it is the streaming 

 movement of the protoplasm in closed cells ; this is known 

 as the " rotation " or the " circulation " of the protoplasm : 

 then there is the contraction of contractile vesicles ; ciliary 

 movement ; amoeboid movement ; and finally the movement 

 of entire organs in the higher plants. 



We have to shew, in the first place, that movement is 

 dependent upon destructive metabolism, and we shall do this 

 in the same manner as in the case of growth: we shall, 

 namely, adduce evidence to prove that conditions which are 

 unfavourable to destructive metabolism also act prejudicially 

 upon the power of movement. 



In regard to growth we found that the presence of oxygen 

 is an essential condition in the case of truly aerobiotic plants ; 

 this holds good, and for the same reasons, with regard to 

 movement. Dutrochet observed that the motile leaves of 

 Mimosa pudica, the Sensitive Plant, lose their power of move- 

 ment in vacuo : Kabsch confirmed these observations and 

 extended them to the motile stamens of Berberis, Mahonia, 

 and Helianthemum, and found further that their movements 

 are arrested in an atmosphere of nitrogen or of hydrogen : 

 Pfeffer, too, observed that the stamens of Centaurea Jacea 

 lost their power of movement after being kept for one minute 

 in an atmosphere of carbon dioxide : Kuhne ascertained that 



