PLATE I. — Syntrophism among arginine requiring mutants of 

 Esch. coli. Mutant O responds to ornithine, citrulline or 

 arginine; C to citrulline or arginine; A to arginine only. 

 Photograph of growth after 48 hr. at 37° C. on a medium 

 containing suboptimal amounts of required nutrients. Note 

 the enhanced growth of C and O due to the secretion by A 

 of a substance (citrulline?) which can be utilized by C and O. 

 Similarly the enhanced growth of O due to the secretion by 

 C of a substance (ornithine?) utilized by O [7] 



