CHAPTER XIII. 



MOVEMENTS. 



1036. MOST of the movements exhibited by plants are asso- 

 ciated with growth. In the preceding chapter attention has 

 been called to some of these movements, especially those which 

 are characterized by a change in the direction of growing 

 parts (see Gcotropism, Heliotropism, etc.). In the present 

 chapter it is proposed to examine continuous and recurrent 

 movements, and indicate to what extent these are likewise the 

 accompaniment of growth. 



In the existing state of knowledge no satisfactory classifica- 

 tion of the movements of plants can be made. The provisional 

 one now to be followed is adopted only for convenience. 



1037. Locomotion, or movement of the whole organism from 

 place to place, can be observed in some of the lower plants. 

 One of the most interesting examples is furnished by ^Kthalium 

 septicum, which at certain stages of its existence consists of 

 approximately pure protoplasm in a naked state. Under favor- 

 able conditions this naked mass (the plasmodium), which fre- 

 quently attains considerable size, passes in a creeping manner 

 over a moist surface, thrusting out processes in an apparently 

 irregular manner, sometimes retracting them, but more often 

 bringing up to the advanced part the rest of the uneven mass. 



The sensitiveness of this mass to the action of external influ- 

 ences renders it a suitable object for the examination of the 

 essential properties of protoplasm, and man}* of the more im- 

 portant facts relative to its movement have therefore already 

 been given (see 550). It is important to notice particularly that 

 there is a rhythmical pulsation of the sap-cavities or vacuoles in 

 the plasmodium, dependent, it is supposed, upon the irregular 

 absorption of water with a varying imbibition power. This spon- 

 taneous pulsation is somewhat affected by external conditions ; 

 for instance, it is increased in rate by heat and diminished by 

 cold. 



1038. Portions of protoplasmic matter concerned in the repro- 

 duction of many of the lower plants, especially those which 



