346 VEGETABLE PHYSIOLOGY 



In many cases the adaptation in question takes the form 

 of a spontaneous movement, in which the living substance 

 is concerned in a manner resembling the muscular con- 

 traction so characteristic of animal protoplasm. In others 

 the response to such changes presents itself to us as a 

 modification of the normal behaviour of the living substance 

 with regard to the vital processes we have examined, and 

 in particular to the entry of water into the vacuoles of the 

 cells or its transmission outwards. 



When we examine the phenomena of movement we 

 find that though evidence of contractility is procurable, 

 this phenomenon is of somewhat rare occurrence in plants. 

 Certain plants at particular times 

 emit from their body small masses of 

 naked protoplasm which are furnished 

 with a varying number of long fila- 

 ments (fig. 149). These filaments, 

 which are protoplasmic also, are 

 ordinarily in a state of active vibra- 

 FIG. 149. ZOOS'PORE OF tion, causing currents in the water 



Ulothrix. x 500. . , . , , , , . 1-1/3 J.T 



in which they live, which float them 

 quickly from place to place. Among these free-swimming 

 protoplasts may be mentioned the zoospores of the Algae 

 and Fungi, and the anther ozoids of these and higher plants. 

 The movement is a spontaneous one, the organisms being 

 endowed with the property of locomotion, which they exer- 

 cise in the discharge of their ordinary life-work. Though 

 put forth in the absence of any external stimulation, the 

 protoplasts are capable of receiving such impulses and 

 modifying the vibratile action accordingly. 



The mechanism of the movement is probably the con- 

 traction of each side of the filament or cilium alternately, 

 or of the part of the cell just at the point of attachment. 

 The impulse leading to the movement must be sought in 

 some decomposition originating in the protoplasm itself, 

 and not excited by any stimulation from without. The 

 phenomenon is often spoken of as ciliary motion. 



