332 



BACTERIAL DISEASES OF PLANTS 



second week. As in many other diseases (see No. V), once a 

 few plants are infected, the gardener's hose is a ready means of 

 distribution to others (Fig. 255), just as a driving rain (Faul- 

 wetter) is in the open field. 



FIG. 253. Photograph of three surface colonies of Bacterium mah'acearum, 

 the middle and right of which were windowed conspicuously on the fourth day 

 (see Fig. 256). These colonies also show the pale rim. Several buried colonies 

 are also visible. X 7. The lines are pencil marks on the bottom of the plate 

 indicating to the photographer the colonies to be photographed. 



Before trying isolations from leaf-spots we always plunge 

 the leaf momentarily into 1 : 1000 mercuric chlorid water to 



FIG. 254. Bacterium malvacearum. Agar-poured plate of March 22, 1915. 

 Photographed March 25. Typical transient mottling. From the Arizona 

 cotton. X 14. 



discourage surface organisms, but the exposure should never be 

 for more than 20 to 60 seconds. The piece may then be thrown 

 into sterile water and rinsed (always briefly, lest the poison 



