6 SYMBIOSIS 



in turn gains more assured perpetuation by the baits it offers 

 for the insects' allurement. The conclusion to be drawn is that 

 Symbiosis is responsible for new and improved economic and 

 genetic values. In the course of evolution the range of symbiotic 

 relations has steadily expanded, the partners betaking themselves 

 to wider fields of action though maintaining their essential 

 economic union, i.e., "non-attached" Symbiosis. The joint 

 evolution of plant and animal progressed au fur et a mesure as the 

 symbiotic output of mutually valuable substances increased. 

 It is an acknowledged fact that the status of a plant is in 

 accordance to its output of valuable substances, i.e., of biological 

 capital. 



An increasing number of biologists look upon the relation of 

 the elements of protoplasm as essentially of the nature of 

 Symbiosis, i.e., as a " partnership " of " life-elements." The 

 principle of partnership, therefore, is very fundamental ; and, 

 the more and the better it is applied by the organism, the richer 

 in desirable factors becomes the protoplasm. The wider, i.e., 

 the non-attached forms of Symbiosis, may thus justly be viewed 

 as legitimate extensions of the most fundamental principle of 

 organic life, namely, that of partnership, involving " live and 

 let live." 



It is a remarkable fact, connected with plant-animal Symbiosis, 

 that a plant stimulus is required by many animals in reproduction. 

 This I believe to be connected with the fact usually expressed 

 by saying that the " kingdoms " are mutually complemental. 

 In reality, plant and animal are inter-dependent and stand in 

 a relation of Symbiosis to each other. They are co-evolved and, 

 as Darwin long ago apprehended, descended from a common 

 progenitor. 



The marvellous genetic purposes to which the bee tribe puts 

 the surplus productions of the plant in " manufacturing " honey, 

 are by no means unique cases of symbiotic adaptation as might 

 be thought ; for many other animals also require the vital symbiotic 

 stimulus of plant pabulum in one form or other. In the interesting 

 case, typical of many others, of the plant-animal Convoluta 

 roscoffensis, the " attached " Symbiosis is so intimate that, as 

 Prof. F. Keeble has shown, the egg-production ceases as soon as 

 the plant partner (the green cell) is unable to do its share of work 

 through being deprived of light. Moreover, if Convoluta 

 roscoffensis is robbed altogether of its (" infecting ") green cells, 



