188 BACTERIAL DISEASES OF PLANTS 



media, and there are at least two strains: one of which splits 

 fats (cream, etc.) with the formation of an acid (var. asiaticum 

 EFS). The flagella are rather hard to stain (Fig. 134). It keeps 

 best in milk, or htmus milk. 



Technic. — Because in the host plants the parasite is promptly 

 followed by saprophytes which often supplant it, cultures are 

 best made a.t some distance from the ground and out of parts 

 recently diseased. It is a rather difficult organism for the 

 beginner to isolate, owing to the fact that while it grows readily 

 on agar-poured plates, the colonies during the first week re- 

 semble those of various saprophytes, so that only after some 

 days can they be picked out easily by the beginner, i.e., when the 

 brown stain has developed, but then they are apt to have lost a 

 portion of their virulence, or may be dead. The best way is to 

 make transfers early from a whole series of numbered colonies 

 that look hopeful, watch the plates for opalescence in surface 

 colonies, and later discard all sub-cultures except those from 

 colonies which have browned properly. The organism may be 

 kept in agar, milk, sugared peptone water, etc., but transfers 

 should be made as often as once every 2 or 3 weeks, and the 

 tubes should be kept in a cool box. It is a good plan also to pass 

 the organism frequently through susceptible plants that it may 

 retain its virulence. 



For inoculation purposes select young rapidly growing shoots 

 of nasturtium, tomato, potato, tobacco, balsam or sunflower. 

 Inoculate by needle-pricks in various ways, i.e., on leaf -blades, 

 petioles and soft stems, and, for contrast, into hard stems 

 and well-developed leaves. Also drench a soil with cultures 

 (young agar-streak suspensions in water), and plant in it 

 tomatoes or Daturas with broken roots. Those which have 

 stood in the seed-bed rather too long and are large may be 

 used for this purpose. But if one has access to material from 

 the field, diseased tobacco stems, or tomato stems may be used 

 instead of cultures for infecting the soil, or along with cultures 

 as an additional experiment, the diseased plants being buried 

 in the soil a few days before the tomatoes or Daturas are 

 transplanted. 



For successful inoculation the plants should not be too old. 



