SYMBIOSIS 55 



real lesson is that even a degenerate green alga of the 

 group of the primitive Chlamydomonadinece can become a 

 plant complement of the animal C. roscoffensis, a relation 

 which, though lacking in permanence, yet at least provides the 

 indispensable pabulum for sexual reproduction. This shows 

 how ill-advised animals are in general to divorce themselves 

 through bad food habits from direct reciprocity with the 

 A r egetable world. 



The ancestors of both alga and animal at one time no 

 doubt were strictly cross-feeding in their habits. 



Just as holophytic (cross-feeding) plants require different 

 food materials from the soil, so the animals first arisen as 

 particular plant-partners, i.e., from a plant soil require a 

 particular plant-food for their normal purposes of life. 



As evolution progressed, however, the dependence ceased 

 to be as particulate as it was in the beginning, and plants and 

 animals became enabled to strike up most varied inter- 

 relations although perpetual in-feeding, for vital bio- 

 economic reasons, was always abhorred by nature. 



The success of the divorce of an animal species from direct 

 reciprocity with the plant is only apparent, for it is purchased 

 at the expense of physiological capital and of survival- value. 

 Nor can it be denied that ultimately the dependence of 

 " in-feeders " on plant-life is nevertheless very real. In the 

 case under review, C. pwadoxa more markedly than 

 C. roscoffensis presents the pronounced transition from a cross- 

 feeding to a conspicuously "in-feeding" (and surfeiting) 

 habit. To say that its dependence on a particular plant-food is 

 less absolute than that of C. roscoffensis is not saying much in 

 its favour, biologically considered. This kind of independence 

 (from biological symbiosis) is in all cases too dearly purchased, 

 i.e., it is only gained at the expense of those values which 

 constitute more particularly the physiological capital of a 

 species. " Freedom with Virtue takes her seat." C. paradoxa 

 also bears out strikingly the truth that an "in-feeding" type 



