AN ANALYSIS OF SYMBIONT REACTIONS 99 



to be some sort of an accompanying organization necessary 

 if chlorophyl is to produce starch. This "organization," 

 apparently, is present in the chloroplast. What, then, is 

 the nature of this "organization?" Is the chloroplast a 

 living body? We do not know, but we have good reasons 

 to suppose that it is a Uving body. This will be discussed 

 in the following chapter. 



How are bacteria modified in symbiosis? The answer 

 to this question is compUcated by a multitude of varia- 

 tions in the responses of different strains of bacteria. Some 

 of these can hardly be more than guessed at in our present 

 state of knowledge. When a bacterium is subjected to a 

 cytoplasmic environment, a number of factors become 

 operative — physical, chemical, thermal, photic and electri- 

 cal. We know that free-living bacteria may be influenced 

 by the same set of factors. It is a comparatively sunple 

 matter to determine the morphologic responses of bacteria 

 in artificial culture media. We can determine some of the 

 physiological and chemical modifications of microorganisms 

 under these conditions, but corresponding examinations 

 of symbiotic bacteria cannot readily be accomplished. In 

 many instances, bacterial sjanbionts exhibit pleomorphism, 

 but free-hving bacteria may exhibit the same tendency 

 (Reed, '24). The responses shown by some pathogenic 

 bacteria illustrate types of response that may be present 

 among microsjanbionts. 



Pleomorphism or morphologic variation, although not 

 limited to microsymbionts, is commonly present in sjnn- 

 biosis. This has been observed by a number of investiga- 

 tors, and is especially prominent in Bacillus radicicola in 

 the root nodules of legumes. The sjinbiont at the time 

 of invasion is a minute rod-shaped organism. Later it 

 develops into a much larger organism, and becomes forked 

 at one end. Finally it transforms into a comparatively 

 large, globular body. These transformation stages, ap- 

 parently, do not occur in the free-Uving state. 



