GROWTH 11 



It commonly occurs but is by no means 

 indispensable. Nor is it necessary that a 

 differentiation of the organism into un- 

 like parts should take place in order that 

 a process may be called growth. Such 

 differentiation is not observed during the 

 growth of the simplest cells, such as bac- 

 teria, which may have at the beginning 

 all the parts they possess when growth 

 is complete. 



Of especial interest is the assimilation 

 of food and the building up of those sub- 

 stances which are characteristic of each 

 kind of organism. We know that seeds 

 can grow for weeks in the dark, absorb- 

 ing nothing except air and water. Under 

 these circumstances the food which is 

 stored in the seed steadily decreases. A 

 kidney bean grown under such condi- 

 tions may reach a height of four feet and 

 gain in weight more than fifty fold. Yet 

 this great gain in weight is wholly due 

 to the water it absorbs. Its dry matter 

 steadily decreases during the whole pe- 

 riod, undergoing a process of combustion 



