6 Walter H. Burkholder 



work done with these diseases. All cultural characteristics of the patho- 

 genes have been determined under identical conditions (and on the same 

 media), which is an essential precaution in showing similarities and distinct 

 differences. The symptomatology of the various diseases on the bean host 

 has been studied under similar conditions, and the host range for each 

 pathogene determined in a like manner. By following such a procedure 

 it is felt that a certain amount of error has been eliminated which might 

 exist in separate investigations conducted in separate laboratories. 



So far as is known, only one important bacterial pathogene of the common 

 bean has been neglected. Phyt. phaseoli var. sojense, while found primarily 

 on the soj'bean, does produce an infection on the common, or garden, bean, 

 and it is regretted that this organism was not included in the comparative 

 study. Wolf (1924) and Miss Hedges (1924) have reported their investiga- 

 tions on the soybean organism, however, and find that culturally it agrees 

 with Phyt. phaseoli, except for a few minor exceptions. The problem 

 appears to be primarily one of pathogenicity. Several other bacterial 

 pathogenes have been reported as being pathogenic to the bean, but they 

 are ones which are of little importance to this host. Phyt. solanaceara, 

 Phyt. tobaca, and Phyt. aptata might be mentioned in this class. 



METHODS 



In any comparative study, the methods used for conducting the experi- 

 ments are of primary importance. In the following paragraphs are set 

 forth the methods employed in making inoculation experiments and in 

 determining or describing the pathogene in culture. Wherever a deviation 

 from these methods is made, it is mentioned in the text. 



INOCULATION EXPERIMENTS 



For conducting inoculation experiments, plants were grown in a green- 

 house at a relatively high temperature. The common bean (Phaseolus 

 vulgaris) and many of its related species thrive best in a warm atmosphere, a 

 vigorous succulent growth is obtained, and furthermore the plants are not so 

 subject to damping-off as they are at a lower temperature. The clovers and 

 the garden peas are an exception to this rule, and these plants were grown in 

 a cooler house. The greenhouse used for the inoculation experiments on 

 beans had a constant-temperature-control apparatus which held the house 

 at approximately 78° to 80° F., except during bright, sunny days when the 

 temperature would rise to 90° F., or even more, after the steam had been 

 shut off. Under these temperature conditions, infection developed much 

 more rapidly when plants were inoculated with such organisms as Phyto- 

 monas phaseoli and Phyt. flaccumfaciens than at lower temperatures, such 

 as 60° to 65° F. With some of the other pathogenes, as good results were 

 obtained at these lower temperatures but, from observation, infection was 

 in no respect better. Phyt. medicaginis var. phaseolicola appears to spread 



