MOTION 29 



tion, there is no suggestion of nuclear 

 or cell division, yet life may go on for 

 many years. 



In view of these facts we must look 

 further for a satisfactory criterion by 

 which living and non-living may be 

 sharply distinguished. 



IV 

 MOTION 



A striking feature of many living or- 

 ganisms is their power of motion. 



In some cases motion is due to growth. 

 The opening and closing of flowers is due 

 to unequal growth of the inner and outer 

 sides of the petals. When the outside 

 of the petal grows faster than the inside 

 the flower closes; when this relation is 

 reversed it opens. In many cases light 

 and warmth are the determining factors, 

 so that some Alpine flowers may open 

 and close two or three times an hour as 

 clouds pass over the sun. 



