428 BACTERIAL DISEASES OF PLANTS 



less for sodium hydrate. There is more growth in +15 than in 

 — 15 peptone bouillon. The optimum acidity for this organism 

 in beef bouillon appears to lie between +12 and +24 on Fuller's 

 scale (1.2 to 2.4 per cent of N/1 acid). 



The bacterium is sensitive to germicides and slowly loses 

 virulence on culture media. It passes over easily (under action 

 of cold, sodium chlorid, or acids) into club-shaped, Y-shaped, 



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^, 



Fig. 326. — Crown gall on Paris daisy. Cross-section of a secondary tumor 

 in a petiole, the result of a pure-culture inoculation on the stem. This has rup- 

 tured to the surface at the top and left side with destruction of the normal tissues. 

 In its center is a tumor-strand connecting it back to the primary tumor. It 

 shows crudely the structure of a stem (wood, cambium, phloem). In the lower 

 part of the tumor are vessels running at right angles to the longer axis of the stem . 



and variously branched involution forms (Fig. 350) which often 

 are dying or dead, i.e., will not grow on agar-poured plates, or 

 come up slowly. These moribund involution forms occur not 

 only in culture media but are common in the tumor, and to them 

 must be attributed not only our former difficulty in isolating the 

 organism, but also the failure of others to isolate it. To keep 

 the organism alive on ordinary culture media, store the cultures 



