AMOEBOID MOVEMENT 121 



fold together, and the whole thing hangs down. This plant 

 also shows that a stimulus applied at one part is transferred 

 to other distant parts, presumably through the protoplasmic 

 threads which connect up the contents of the cells. 



Finally we have movements which are brought about by 

 the contiguity of thick-walled, stiff cells and thin-walled 

 limp cells. Should water be withdrawn from the thin-walled 

 cells they shrink, whereas the thick-walled cells retain their 

 water. This shrinkage causes the leaf to curl up, but it 

 will uncurl when water is supplied to the thin- walled cells. 



Occasionally parts of the plant explode, and this is due to 

 certain cells being extremely weak and feeble, whereas others 

 become extremely tense and turgid. A slight increase of the 

 turgidity will rupture the weaker cells. These explosive 

 movements are often connected with a dispersal of seeds or 

 spores ; the squirting cucumber is an example of the former, 

 and in fact many fruits exhibit this action. The common 

 geranium and the violet jerk out their seeds, and at times the 

 explosion is accompanied by an audible sound. Plants are 

 as a rule mute: no one expects a mushroom or a beech tree 

 to burst into song. They have the great gift of silence, and 

 when they do make a noise it is a momentary pop and is 

 seldom repeated. 



Amoeboid Movement 



Amoeboid movement is to be seen in almost every group 

 of the animal kingdom. In the protozoa many animals other 

 than those classed with Amoeba itself are amoeboid at certain 

 stages of their career. In the higher animals there are many 

 cases of this form of movement; the cells lining the alimentary 

 canal of the Coelenterata and of the Turhdlaria are often 

 amoeboid; the nerve-fibre or axon of a developing nerve 

 reaches its destination by amoeboid movement; almost every 

 group of animals have amoehocytes or wandering cells which 

 exhibit amoeboid activity. 



How does amoeboid activity take place? All that we can 

 observe is that the protoplasm of Amoeba is capal)le of 

 great changes of shape although there is no visible internal 

 contractile mechanism such as the fibrillar structure observed 



