494 SCIENCE PROGRESS 



forms of life and in the more complete development of beneficial 

 relations between them. 



/. What is Symbiosis ? 



W . It is usually defined as a physiological partnership 

 between organisms of different species. 



/. Is this " partnership " productive of economic, genetic, 

 and social gains in a real and permanent sense ? 



W . It is primarily economic. When the association be- 

 comes sufficiently systematic and intimate, it conduces to 

 pronounced physiological effects affecting sex, structure, status, 

 and biological correlations. 



I. Can you give an instance ? 



W . The lichen presents a symbiotic association between an 

 alga and a fungus, a union calculated to meet by mutual effort 

 the economic problem of existence where by single efforts it 

 could not so well be met. Systematic economic co-operation 

 in this case of " attached " Symbiosis has led to a high degree 

 of reciprocal adaptation and reciprocal differentiation in the 

 physiological economy of the organisms concerned. Indeed 

 the physiological reciprocity has here become so intimate that 

 it required years of painstaking research and of controversy 

 to establish the fact of the compound and dual nature of the 

 lichen. It has since been shown that the reproductive organs 

 of the lichen are of a typically fungal character, i.e. the repro- 

 ductive function could be deputed more specially to one of the 

 associated organisms, whilst the other specialised in other 

 important directions (photosynthesis with carbohydrate manu- 

 facture). Symbiosis here is responsible for new and improved 

 economic and new and improved genetic values — important 

 also so far as the correlated world of life is concerned. The 

 lichen is a veritable pioneer of " organic civilisation " ! 



The radius of symbiotic action and reaction, however, has in 

 course of evolution become very much wider than in such 

 " attached " partnerships. The highly specialised partners 

 eventually separated, betaking themselves to wider fields of 

 action though maintaining " non-attached " Symbiosis. Here 

 the effects of mutual stimulations upon the development of sex 

 are no less important. I have demonstrated how in these cases 

 we must look for some of the faetors of inheritance to the symbiotic 

 environment and that they cannot operate unless the symbiotic 

 co-operation is fully carried out. 



