10 THE NATURE OF LIFE 



self in water begins to grow. No one 

 will deny that this is genuine growth 

 but it certainly need not possess all the 

 features which we have enumerated. In 

 the jfirst place cell division may be absent 

 for a long time. Many cells increase 

 enormously in size and never undergo 

 division. A nerve cell may grow to be 

 many hundred times its original length 

 without dividing; and it will continue to 

 function for years and finally die with- 

 out any sign of nuclear or cell division. 

 We cannot therefore regard cell division 

 as essential to the conception of growth, 

 though in most cases it accompanies 

 growth and is advantageous because it 

 provides separate compartments in which 

 the diverse processes of the organism can 

 go on without mutual interference. 



There may be no change of form or 

 color in the green cell of which we are 

 speaking, since it may remain green and 

 spherical while growing. Nor is there 

 any reason to suppose that in general a 

 change of form is essential to gro^vth. 



