S^TVIBIONTICISM AND ORGANIC EVOLUTION 145 



and particularly in connection with diseases. These fac- 

 tors are the forces that influence protoplasmic behavior, 

 such as, temperature, light, moisture, pressure, electricity, 

 and possibly gravity, solar and lunar forces. In connec- 

 tion with disease, and also symbiosis, we do not know 

 whether the host or the microorganism, or both, are modi- 

 fied by these extrinsic influences. Perhaps, when we 

 some day have acquired more specific data on metero- 

 logical influences on living matter, we may then better 

 understand the behavior of living organisms. 



It is highly unsatisfactory, and it invites criticism, to 

 delve into extensive hypothetical analyses and discussions. 

 Nevertheless, it appears to be necessary to predicate scienti- 

 fic progress with speculation. These hypothetical analyses 

 and discussions are not offered as evidence of the reahty 

 of Symbionticism, but entirely in the spirit of demon- 

 strating the rationahty and the feasibihty of the principle 

 of Symbionticism. The evidence for the operation of 

 Symbionticism in the origin of species is to be found in 

 those forms in which the microsymbiont still retains its 

 identity. This was reviewed in the chapter on ''Micro- 

 symbiosis," and it appears to be conclusive. Aside from 

 this direct evidence, we have submitted what might be 

 called ''cricumstantial evidence" which supports the direct 

 evidence. The bacterial nature of mitochondria indicates 

 the universal operation of the principle of Symbionticism. 

 The correlation of bacterial products and the products of 

 speciaUzed cells in plants and animals demonstrates the 

 feasibihty of the principle of Symbionticism in the origin 

 of species. 



Although there was no acceptable evidence of the bac- 

 terial nature of mitochondria at hand when Buchner ('20) 

 wrote his extensive review on microsymbiosis, he, never- 

 theless, recognized its probable significance in the origin of 

 species. The following quotation makes this clear. 



