144 



BACTERIAL DISEASES OF PLANTS 



taining thrifty cucumber plants bearing each about 6 or 8 

 leaves. Remove next morning. Repot the plants and watch 

 closely. The squash bug, Coreus tristis, also may be. tried 

 (but only on well-grown plants because of the great injury 

 done by this bug to small plants). Mr. F. V. Rand believes 

 from his experiments that the squash bug does not carry the 

 disease. For details on insect transmission see Part I, p. 30). 



FIG. 78. Cross-section of a cucumber stem such as Fig. 73 showing the in- 

 dividual bacteria in a small pitted vessel. This was photographed by the writer 

 in 1894 from an unstained glycerin mount using a Welsbach light and an old Zeiss 

 non-apochromatic objective the photographic focus of which was not the same as 

 the eye focus. The duration of the exposure was about an hour and for this pic- 

 ture the negative was enlarged. 



Where does the organism winter-over, i.e., in the soil? 

 in hibernating beetles? or on, or in seeds? From its appearance 

 on leaves in early summer first in places gnawed by Diabrotica, 

 I have long believed that it winters over in the bodies of the 

 cucumber beetles. (See recent observations and experiments 

 by Frederick V. Rand, of my laboratory, in Journal of Agri- 

 cultural Research, Vol. V, November 8, 1915, p. 257; Vol. VI, 

 June 12, 1916, p. 417; Dept, Agr. Bulletin No. 828 (Profes- 

 sional Paper) 1920 and Phytopathology, Vol. 10, No. 4.) 



