BROWN ROT OF SOLANACEAE. 



181 



beetles. In course of a few weeks the plants were destroyed (fig. 87), and the tubers were 

 rotted from within in the same way as when the plants were inoculated by needle-punctures. 

 From this it was concluded that the disease depended for its dissemination very largely on 

 insect-carriers an inference needing further verification. 



All of the writer's successful experiments having been made on leaves and stems, it is 

 likely that in his bulletin too much stress was laid on the possibilities of infection through 

 parts above ground. At that time the writer certainly regarded these as the most vulner- 

 able parts. Burrill's observations led him to the same conclusion. Hunger has since shown 

 that when tomatoes are grown in infected soil, or water, they contract the disease readily 

 if the roots are wounded but not otherwise. His field observations led him to the same 



Fig. 87.* 



conclusion. Observations on tomatoes in Mississippi led Earle to believe that underground 

 infections were very common. Dr. Van Breda de Haan's observations on the slime-disease 

 of tobacco in Sumatra led him to the same conclusion. I have also obtained underground 

 infections on both tomato and tobacco, using the North Carolina tobacco-wilt organism. 

 We may conclude, therefore, that the bacterium can enter readily through wounds made on 

 any part of the plant either above ground or below. In such event the manner of infection 

 would vary from plant to plant and field to field, according to the prevalence of particular 

 insects or other sources of injury. 



Whether the organism can enter the plant in the absence of abrasions must be left an 

 unsettled question. Burrill thought it could. Hunger states that it can not, but his experi- 



*Fig. 87. Potato plant (left) promptly destroyed by Bacterium solanacearum as the result of the gnawings of 

 infected beetles. (See text, p. 184.) Control plant on the right. 



