78 Walter H. Burkholder 



were considered in compiling this table. In all cases, care was taken to 

 make certain that a virulent culture of the pathogene was being used. 

 Nevertheless, when infections on a certain plant were not obtained, the 

 experiment was repeated two and three times to make certain of the 

 results. Even then, some unknown factor necessary for infection might 

 have been absent. However, under the conditions maintained — a tem- 

 perature of 80° C, and the use of young, rapidly growing plants as the 

 host — it is felt that the data are very close to being correct. 



It may be noticed that most of the organisms listed in table 3 show a 

 distinct difference in their ability to infect many of the species of plants 

 considered. Phyt. phaseoli var. fuscans and Phyt. medicaginis var. phaseo- 

 licola, however, have a similar host range as far as the table shows, and 

 Phyt. viridiflava and Phyt. vignae var. leguminophila appear rather closely 

 related in this respect. 



DIFFERENTIATION OF THE BACTERIAL DISEASES FROM OTHER BEAN 

 DISEASES NOT OF BACTERIAL ORIGIN 



The bacterial diseases of the bean will not, as a rule, be confused with 

 any other bean diseases of fungous or of virus origin. There are a few 

 pitfalls, however, which should be considered here. 



The only fungous disease that causes lesions on the stems, leaves, and 

 pods of the bean plant is the anthracnose due to Colletotrichum linde- 

 muthianum. The differences in the character of the symptoms of the 

 anthracnose and of the bacterial blights have been emphasized repeatedly 

 in numerous publications, and need not be described here. Any one 

 who is at all familiar with plant diseases will be able to make the distinc- 

 tion between this fungous disease and bacterial blights. 



The mosaic symptoms on the leaves of the bean plant produced by Phyt. 

 medicaginis var. phaseolicola have been reported earlier in this memoir, 

 and if these are observed alone some difficulty might arise in distinguish- 

 ing them from the mosaic produced by the true virus disease. In examin- 

 ing infected plants as a whole, however, the separation of the two diseases 

 on the basis of the other symptoms should be made very readily. 



Fusarium martii f. sp. phaseoli will cause a stunting of the bean plant, 

 a yellowing and dropping of the leaves, and sometimes a slight wilt. An 

 examination of the roots of plants so appearing, however, would leave 

 no doubt as to the organism causing the trouble. 



Seedling wilts due to the bacteria are indistinguishable macroscopically 

 from the hereditary seedling wilt described in a previous publication 

 (Burkholder, 1926). If the wilt is due to bacteria, the microscope will 

 reveal the cause. Furthermore, the hereditary wilt has never been 

 observed except on hybrid plants. 



Spots on bean pods due to sun scald are often confused with spots caused 

 by bacteria. On certain varieties of beans, especially the garden varities, 



