SYMBIONTICISM AND ORIGIN OF SPECIES 111 



the blue-green algae presupposes a morphologic reaction, 

 upon the acquisition of the symbiotic relationship. This 

 is in harmony with the usual reactions observed in micro- 

 symbionts. Furthermore, it harmonizes with the adaptive 

 behavior of Hving organisms in general. 



Merejkovsky ('20) has recently advanced the hypothesis 

 that the chloroplast is a microsymbiont, genetically related 

 to the blue-green algae, and that all the higher green plants 

 are symbiotic complexes. He has emphasized the morpho- 

 logic and physiologic similarity of chloroplasts to the 

 Cyanophyceae. It appears, from an analysis of Merejkov- 

 sky's treatise, that he could not harmonize a mitochondrial 

 origin of plastids in plant ontogeny with a genetic origin 

 from the Cyanophyceae. He does not believe that the 

 plastids originate from mitochondria in the ontogenetic 

 development of the plant. In lowly forms hke the algae, 

 it is possible for the plastids to divide and multiply as such; 

 the transmission of microsymbionts in algae from one gen- 

 eration to another is a comparatively simple matter. In 

 the higher plants reproduction is compUcated, and the 

 transmission of an absolute symbiont must be associated 

 with the germ cell or its accessory parts. The potentiali- 

 ties of the entire plant are crowded into the germ cell; it is 

 not surprising therefore to find the symbiofit also modified 

 for transmission. While we agree with Merejkovsky's 

 conception of the symbiotic nature of all the green plants 

 (we would extend his conception to include all plants), 

 we cannot agree with his rejection of the association of 

 mitochondria in ontogenetic chloroplast formation. The 

 careful researches of Guilliermond and others, appear to 

 have definitely established this relationship. Merejkov- 

 sky, perhaps has been misled by the assumed fixed phospho- 

 lipin constitution of mitochondria. 



The question may arise, — Under what circumstances 

 does Symbionticism take place? It is impossible to give a 



