THE CUCUEBIT WILT: CAUSE 



135 



viscid, capsulate, motile, white, 

 non-sporiferous, slow-growing, non- 

 liquefying, non-milk-curdling, non- 

 nitrate-reducing, non-gas-forming, 

 aerobic and facultative anaerobic 

 (acid-producing), rod-shaped, peri- 

 trichiate schizomycete (Fig. 68), 

 forming on the surface of agar- 

 poured plates, internally reticulated 

 (Figs. 69, 70), small, circular 

 smooth, wet-shining (Fig. 71), 

 colonies. It is easily killed by 

 heat, by dry air and by weak 

 acids. It must be transferred very 

 frequently on culture-media. It 

 may be kept alive longest in milk 

 or in sugared peptone water over 

 calcium carbonate. It does not lose 

 virulence quickly. There are at 

 least two strains, to one of which 

 (f. cucumis EFS.) the squash is im- 

 mune. 



Technic. — If the organism to be 

 used in the inoculations must be 

 isolated from old stems, wash the 

 stem thoroughly in clean tap water, 

 select a middle part, roll around 

 quickly two or three times in a 



Fig. 67. — Secondary (general) bacterial 

 wilt of a cucumber vine as the result of bites 

 of the striped beetle {Diabrotica vittata) after 

 it had fed on a bacterial culture. These 

 bites, few in number, were on the lower leaves 

 and resembled those shown in Fig. 66. The 

 infectious material was obtained by the 

 beetles from leaves of other cucumbers where 

 I had placed it a few hours before in making some needle-prick inoculations. 

 Beetle-bites both on my inoculated leaves and on those of this plant were dis- 

 covered next morning and the disease was predicted. It developed around the 

 bitten places in the usual time and progressed just as on the pricked plants. 



