500 MICROBIAL DISEASES OF PLANTS. 



usually be accounted for by inoculation by plant lice and the pear twig 

 borer. 



CAUSAL ORGANISM. According to Jones* Bacillus amylovorus possesses the 

 following characteristics: Short motile bacillus, rounded ends, ifj.-i.8fi by 0.5^-0.9^; 

 stains readily with the aqueous stains; Gram-negative. No spores observed. 



Agar slant and potato, growth moderate, filiform, glistening, smooth, grayish white, 

 semi-opaque, butyrous. Gelatin stab, growth rather slow, filiform, slight crateriform 

 liquefaction after twenty days. Nutrient broth, moderate clouding, uniform; if left 

 undisturbed, a delicate pellicle or ring may form which breaks up and sinks with the 

 slightest jar; scant finely granular sediment after ten days. Litmus milk, light blue in 

 four days, pinkish in six days, light blue again in twelve days, upper layer blue in eighteen 

 days; soft gelatinous curd six to ten days, with whey on the surface. Cohn's solution, 

 no growth. Uschinsky's solution, no growth. Nitrates not reduced. No indol. 

 Thermal death-point 50. Optimum temperature 23 to 25. Slight acid production 

 but no gas from dextrose, etc. Starch is not fermented. 



CONTROL. It is obvious that spraying is useless for a disease of this 

 character, where the germs are located beneath the surface. 



A systematic cutting out of the diseased limbs and twigs wherever and 

 whenever they appear is the only practical method of controlling the blight. 

 It is almost impossible to get all of the diseased material in the summer time 

 when the heavy foliage hides it, but in the fall and winter the blighted 

 branches can be recognized very readily by the tufts of dead leaves cling- 

 ing to them. It is necessary in removing the dead wood to cut well below the 

 discolored part, ten to fifteen inches, for the bacteria may be considerably 

 in advance of the discolored area. Clean out all old cankers by cutting 

 well into the healthy part and by removing the dried, diseased material. 

 Disinfect the freshly cut surfaces of this wound as well as the exposed 

 ends of twigs and limbs with T-IOOO solution of mercuric chlorid. All 

 diseased wood must be collected and burned. 



TOMATO BLIGHT. 



Bacterium (?) michiganense Erw. Smith. f 



This disease is distinct from the wilt, caused by B. solanacearum, in 

 that there is not the sudden collapse of the whole plant, but rather a slow 

 yellowing or wilting of the leaves, one at a time. The causal organism 

 produces cavities in the pith and bark as well as in the vascular system. 



* Jones, D. H.: The Bacterial Blight of Apple, Pear and Quince Trees. Bull. 176, Ontario 

 Agr. College. 



t Smith, Erw., Science, N. S., Vol. XXXI, 803, p. 794. 1910. 



