GROWTH. 157 



simple or direct form of growth common to crystal and to 

 simple organic individuals of the first order. This simple 

 form of growth is secondarily opposed to compound or 

 numerical growth, which is seen in the course of the evolu- 

 tion of all many-celled organisms, in all individuals of the 

 second, or higher order. In this case, the simple cell does 

 not continually increase, as might be supposed, until the 

 whole large organic individual, with all its parts, is formed; 

 but after the cell has attained a certain, very limited size, 

 it does not increase further, but parts by self-division into 

 two cells. Owing to the frequent repetition of this pro- 

 cess of compound growth, a many-celled organism, which 

 is far larger than the largest cell, at last arises. In this 

 case, the growth of the ever-increasing organism is no 

 longer the mere addition of homogeneous parts, but depends 

 really on generation, i.e., the multiplication of the origin- 

 ally simple individual. 



A further distinction between organic and inorganic 

 growth depends on the fact that the former, unlike the 

 latter, is connected with nutrition. Nutrition is necessary 

 to the existence of every living organism, for loss of sub- 

 stance of body-material is implied in all life-energies ; and 

 this loss of substance must be replaced by the addition of 

 new substance or food. This continual change of sub- 

 stance, the absorption and assimilation of new matter, 

 the expulsion of used-up particles, and briefly, all the 

 processes included by the term. nutrition, are conditions 

 as necessary to the accomplishment of evolution as for all 

 the other activities of life : they are as indispensable to the 

 evolution of the single cell as to that of the entire many- 

 celled organism. The usual method of nutrition in the 



