18 SYMBIOGENES1S 



always be on the work and, more particularly, on the surplus 

 products of the plant kingdom, I have been at some pains to 

 point out in previous volumes. 



The fact that plant and animal are physiological and bio- 

 economic complements itself, indeed points to a common 

 origin, as Darwin has already suggested from analogies of 

 descent. We may take it that at one time in the common 

 progenitor the respective units stood in a relation of reciprocal 

 differentiation to one another, much in the same way as the 

 relations between the organs of the body, or between the two 



For aeons of time, we may believe, they were thus enabled 

 to gain experience in mutuality and in (unconscious) co-opera- 

 tion. The better the vegetable part functioned in providing 

 free oxygen and other reserve material, the better the animal 

 part could function in setting free carbon-dioxide, in restoring 

 certain nitrogenous products, and in evolving new substances 

 for future mutual use. To be eternally providing not only for 

 the present but also for a more glorious future, is quite as 

 much a feature of the eternal giver, which is the plant, as is 

 its much-talked-of passivity. Finally, in the evolution of the 

 plant-animal, with increasing specialisation and differentia- 

 tion, we may assume a separation of the partners to have taken 

 place, much the same again as in the case of the sexes. The 

 separation, however, is merely superficial, and we need to bear 

 in mind that essentially every animal remains a plant-animal 

 and every plant an animal-plant. Both are to increase the 

 efficiency of reciprocal arrangements though separate. When 

 separation came it only meant that both partners had qualified 

 for work in wider spheres. 



The primordial bio-economic and combined physiological 

 relations essentially continued the same and remained as indis- 

 pensable as before. With greater opportunities there arose 

 greater possibilities of excess, and, organisms being physio- 

 logically frail, they have usually fallen victims accordingly. 



