190 INDIVIDUALITY IN ORGANISMS 



central nervous system, the most stable structure physi- 

 ologically of the body, and in the other its persistence 

 indefinitely as an embryonic cell or a group of cells, must 

 be an expression of the fundamental difference between 

 the two groups of organisms. Evidently this difference 

 is primarily a difference in relation between the proto- 

 plasmic substratun^ and the metabolic reactions. Stable 

 morphological structure and differentiation in the plant 

 consist largely in the deposition of carbohydrates and 

 other non-proteid substances within or about the cells, 

 while in the animal morphological differentiation very 

 generally has its origin and foundation in the accumula- 

 tion and specialization of protoplasm itself. Apparently 

 the protoplasmic substratum of the plant is much less 

 stable physiologically than that of the animal. The 

 plant seems to be incapable or almost incapable of syn- 

 thesizing proteid molecules which are physiologically 

 stable where the metabolic rate is high. The protoplasm 

 of the plant cell is certainly much more directly and 

 intimately involved in the chemical reactions of metab- 

 olism than that of most animal cells; consequently 

 in regions of high metabolic rate no persistent proto- 

 plasmic structure like that of the animal cell can arise, 

 because there is no accumulation of relatively stable 

 substances in the cell. In regions where the metabolic 

 rate is lower, substances may accumulate in the cell 

 as structure which with a higher metabolic rate would 

 be decomposed. In the plant, therefore, morphological 

 differentiation increases with increasing distance from 

 the growing tip and decreasing metabolic rate, while 

 in the animal differentiation begins and is most stable 

 in the apical region — the region of highest reaction rate — 



