46] CHAPTER III. SPECIAL PHYSIOLOGY OF MOVEMENT. 205 



strated by the fact that any change which prejudicially affects 

 the activity of catabolism, similarly affects the dissipation of 

 energy. For instance, in the absence of free oxygen, a condition 

 which" diminishes catabolic activity in most cases, germinating 

 seeds or opening flowers cease to evolve heat ; the luminous Fungi 

 cease to emit light ; growth, and the other more conspicuous 

 movements are arrested : similar effects are produced by exposure 

 to a low temperature. 



CHAPTER III. 



SPECIAL PHYSIOLOGY OF MOVEMENT. 



46. Introductory. The movements to be specially con- 

 sidered here are such as may be characterized as vital ; that is, 

 they are essentially manifestations of the life of the protoplasm. 

 This statement is rendered necessary by the fact that movements 

 do occur in plants which are dependent upon purely physical 

 causes ; instances of these are afforded by the rupture of pollen- 

 sacs and other sporangia, the twisting and untwisting of awns (as 

 in the fruits of Erodium and Stipa), the bursting of fruits (as 

 in the Balsam, Impatiens Noli-me-tangere, and the Squirting 

 Cucumbers, such as Ecbalium, Momordica, and Elaterium). These 

 movements may be due, in the simpler cases, either to expansion 

 and contraction of hygroscopic cell-walls resulting from variations 

 in the moisture of the air, or to the imbibition with water and the 

 consequent swelling-up of mucilaginous substances in the cells ; 

 in the more complicated cases the movement depends upon tensions 

 set up between different layers of tissue in consequence of unequal 

 expansion. 



The vital movements are either spontaneous or induced. In the 

 former case they are the result of causes operating in the organism 

 itself ; in the latter, they are the result of causes acting upon 

 the organism from without. 



The following are the principal phenomena of movement ex- 

 hibited by plants ; the streaming movement of protoplasm 

 (cyclosis) ; the expansion and contraction of contractile vacuoles ; 

 the locomotion of entire organisms ; the movements of cellular 

 members. 



