SITVIBIONTICISM AND ORIGIN OF SPECIES 109 



bear a close morphologic similarity to the blue-green algae 

 (Cyanophyceae) . Physiologically the two structures are 

 also similar. The possible phylogenetic origin of plasts 

 from the blue-green algae appears to be a logical conclusion 

 in line with Symbionticism. How are we to harmonize the 

 mitochondrial origin of plasts in ontogeny with a relation- 

 ship to the blue-green algae? Are the plasts to be con- 

 sidered transformations of symbiotic " bacteria? It must 

 be mentioned in this connection, that a large number of 

 bacteriologists claim that no bacteria are known which 

 contain chlorophyl; other bacteriologists, on the other 

 hand, insist that chlorophyl is present in some forms. A 

 number of circumstances and experiences, however, assist 

 us in correlating and harmonizing the plasts with Symbion- 

 ticism. It has been shown in microsymbiosis, and particu- 

 larly in the behavior of mitochondria, that microsymbionts 

 may be altered by 'their environment. The mitochondrial 

 pleomorphism experiments clearly demonstrated the pleo- 

 morphic responses of these microorganisms to shght varia- 

 tions in the environment. The absence of chlorophyl in 

 the mitochondrial stage of the chloroplast is not a barrier 

 to the acceptance of a genetic origin from the blue-green 

 algae. It was shown in cormection with the development 

 of the luminous organ in some squids, that luminous bac- 

 teria were not present until the organ was completely 

 formed. Extrinsic factors as well as inherent tendencies 

 operate in the development of "specificity" in microorgan- 

 isms. It has been shown also by various investigators, 

 and is commonly accepted that hght is a fundamental 

 factor in the production of chlorophyl. 



These observations and experimental results certainly 

 indicate reactions and processes in microorganisms, par- 

 ticularly microsymbionts, that clear the way for a better 

 appreciation of the possible genetic relationship of chloro- 

 plasts and the blue-green algae. It may appear that the 



