SYMBIOSIS AND THE BIOLOGY OF FOOD 263 



of Divergence of Character. He showed that diversification 

 is a useful alternative to close competition, that the greatest 

 amount of life can be supported by great diversification of 

 structure, and he indicated that a carnivorous quadruped, for 

 example, may become more successful by becoming less car- 

 nivorous. In his own words : " The advantage of diversifica- 

 tion of structure in the inhabitants of the same region is, in 

 fact, the same as that of the physiological division of labour in 

 the organs of the same individual body." 



Parenthetically, I would here remark on the fact, observable 

 throughout nature, that occasional abstemiousness from food 

 and an occasional conversion from a carnivorous to a vegetarian 

 nutrition, are usually followed by beneficial effects upon the 

 species. My explanation is that by such means co-operation 

 and general symbiotic integrity are apt to be restored, with the 

 result that plasticity and rejuvenescence are again safeguarded. 

 In other words, the abstemiousness signifies a " good " diver- 

 sification, one that approximates the general restraint normal 

 to Symbiosis. 



The plant can assist symbiotic diversification with increasing 

 reliability the more it is in turn supported by symbiotic 

 contributions from the animal. In the above example, the 

 reliability of the alga is undoubtedly the greater the more the 

 alga can in turn rely upon constancy of supplies of carbon 

 dioxide from the animal. And it is constant and systematic 

 services which count in industry. If, in the natural scheme of 

 things, the plant was to become increasingly a manufacturing 

 specialist, and if the animal was to become increasingly a 

 complemental specialist, this desideratum could have been 

 achieved on condition only that the mutual relation between 

 plant and animal remained in all essentials symbiotic. Which 

 is also saying that the respective appetites had to remain 

 essentially restrained in accordance with the requirements of 

 Symbiosis, and, further, that the healthiness of the joint 

 evolution of plant and animal, and the health of plant and 

 animal individually, depended upon persistent Symbiosis — 

 matters to which I attach the utmost importance. 



In my opinion, the life of the flora is so interdependent with 

 that of the fauna that separate study can scarcely conduce 

 to a full understanding. If we cannot have the widest possible 

 view of evolution, it would often be better to have none at 

 all. The plant, then, we may take it, has steadily increased 

 and improved its yields, in proportion as it was able to rely 

 upon an increasing adequacy of animal counter-services. It is 

 recognised that the status of a plant in the evolutionary scale 

 is in accordance with its output of useful substances ; but we 

 must likewise recognise that the status of the animal is com- 



