238 BACTERIA IN RELATION TO PLANT DISEASES. 



the planting on such fields during the interim of other crops which might act as carriers 

 of the disease, or on the condition of the seed-bed from which this field was set. (For infection 

 of a cabbage field with Bad. campestre from a seed-bed see this monograph, Vol. II, p. 329.) 



From these statements it is evident that under favoring conditions this disease may 

 prove very detrimental to tobacco-culture. 



The reader will gather from what precedes, to recapitulate: (i) that only sound plants 

 should be set out, and to this end the seed-bed should be on soil free from this organism; (2) that 

 seedlings should be transplanted early and injured as little as possible in the removal; (3) that 

 they should not be watered from infected wells, ponds, or streams; (4) that diseased plants 

 should be removed from the fields as promptly as possible, so that they may not become centers 

 of subsequent infection; (5) that the fingers or knives should not be used on sound plants after 

 use on diseased plants without a preliminary sterilization; and, finally, (6) that as far as 

 practicable, badly infested fields should be devoted to other and non-solanaceous crops. Toma- 

 toes, potatoes, peppers, or egg-plants must not follow the tobacco, nor should peanuts. 



THE JAPANESE DISEASE. 



In 1904, Uyeda described a Japanese tobacco -disease which seems to belong here, at 

 least so far as signs are concerned. He says: 



This disease causes much damage in Japan, especially in those cases in which the transplantation 

 from the seed-bed is carried out rather late. Prolonged moist weather with following great heat will 

 cause the development of the disease. The first symptom is the wilting and yellowing of the lower 

 leaves, then follows the blackening of the stem and leaves, and finally of the root. The plants are 

 generally killed in about two weeks after the first symptoms are observed. The natural infection 

 seems to take place generally through the roots, but very frequently also by the wounds caused by 

 topping and suckering the plants toward the end of July. A microscopical examination reveals an 

 immense number of bacteria in almost a state of pure culture in the vascular bundles. The central 

 part of the stem shows a rotten condition and contains a dark brown liquid. Finally the stem becomes 

 hollow and the root is completely destroyed. 



The organism, it is said, was cultivated pure, apparently in bouillon, and infections are 

 said to have been obtained in about 2 weeks by irrigating healthy tobacco plants in pots 

 and in the field. Infections through the stomata are also said to have been obtained by 

 spraying a pure culture of the organism upon healthy leaves of young tobacco plants about 

 25 cm. high, but no evidence of this is offered other than that after 8 days a blackening was 

 observed along the veins of the leaves, which extended more and more, and a microscopical 

 examination showed enormous numbers of bacteria in the pitted vessels. Egg-plants which 

 were irrigated in the same way as the tobacco did not contract the disease. This, however, 

 might have been due to old and woody stems (see p. 236). 



This organism is described as Bacillus nicotianae and is said to have the following 

 characteristics : 



Agar-stabs and streaks blacken, especially in the parts exposed to air (fig. 127). 

 Growth on gelatin in streak-culture is very slow, forming a uniform pellicle, white at first, 

 gradually blackening, with feeble liquefaction of the gelatin after about 5 weeks. Gas is 

 produced in glucose agar and glucose bouillon, and there is a rancid smell, but only a little 

 acid is formed. Milk is cleared. On potatoes it produces a yellow pigment, gradually 

 turning brown-gray. In colonies on agar the growth is dirty white: gradually the brown 

 pigment is produced, diffusing beyond the colony, which itself remains generally gray and 

 shows concentric rings as it enlarges (fig. 128). Growth is best at 32 C. The organism 

 is facultative anaerobic. It produces no odor in peptonized bouillon. It is 0.6 to 0.9/4 

 by i to 1.2/j long. It is said to bear about 8 peritrichiate flagella. 



