DISEASES OF PLANTS. 685 



established, however, until the disease has been artificially produced by the inocula- 

 tion of healthy plants. Various methods of carrying on investigations are suggested, 

 and notes given as to the length of time which the organisms are able to survive in 

 the soil. 



As means of preventing loss, the authors suggest the destruction of the diseased 

 plants, great care in preventing infection through soil carried on implements or the 

 feet of animals from infected to other fields, crop rotation, and the jjlanting of 

 resistant varieties of tobacco. 



The wilt disease of tobacco and its control, R. E. B. McKenney ( U. S. Dept. 

 Agr., Bureau of Plant Industry Bui. 51, pt. 1, })p. 6, fig. 1). — A description is given of 

 the wilt disease of tobacco, which has been under observation for some time in North 

 Carolina. The disease makes its appearance when the tobacco plants have attained 

 about one-third of their growth, and the first evidence of the disease is the sudden 

 wilting or drooping of one or more of the leaves. This is followed by the wilting of 

 other leaves, and later the stem blackens and rots, the plant being destroyed. 



The cause of this disease is said to be similar to that which causes the wilt of cot- 

 ton, watermelon, and cowpea and, as shown by comparison with these diseases, the 

 Fusarium to which the disease is attributed, gains entrance to the plant through the 

 fine roots. It is a soil fungus, and for its eradication all diseased plants should be 

 collected and burned. Tobacco and other susceptible crops should be cultivated in 

 long periods of rotation, and as an additional means of getting rid of the fungus in the 

 soil the author recommends autumn plowing and burning of the stubble. Breeding 

 resistant varieties is thought to possibly be of value and experiments along this line 

 are under way. As an additional precaution it is recommended that no fertilizers 

 containing kainit or muriate of potash be used. Observations and experiments on 

 this disease are being continued, and it is hoped that some definite method of con- 

 trol may be discovered in the near future. 



The mosaic disease of Sumatra tobacco. I, Report of experiments con- 

 ducted at Deli during 1901-2 on the mosaic disease, F. W. T. Hunger {Meded. 

 'aS Lands Plantentuin, 1903, No. 63, pt. 1, pp. 108). — The report is given in 3 chapters, 

 covering the field work, the laboratory work, and the discussion of remedies and 

 preventives, respectively. 



The field experiments were designed to show whether various methods of treating 

 the seedlings and mature plants did or did not influence the occurrence of the dis- 

 ea.se. A number of seedlings were transplanted 1, 2, or 3 times before being finally 

 planted in the field, but it was found that this had no effect upon the occurrence of 

 the disease. Seedlings that were pulled while the soil was dry and transplanted 

 were afterwards more seriously affected than seedlings that were pulled out of wet 

 soil. 



At different ages plants were topped to determine the effect of this operation upon 

 young and older plants. It was shown that of plants topped at 3 weeks of age the 

 percentage of diseased plants was less than when the plants were topped at 6 weeks 

 of age. But it also developed that out of 1,200 plants on new ground not one devel- 

 oped the disease, though they were topped at ages varying from 2 to 6 weeks. 



Cuttings from healthy and from diseased plants were rooted. Those from the dis- 

 eased plants did not flourish and all developed the disease, but while those from the 

 healthy plants grew well every plant subsequently became diseased. When scions 

 from diseased plants were grafted upon healthy stems the old leaves on the healthy 

 stems did not become diseased, but all the new growth on the old stems was diseased. 

 Scions from healthy plants grafted upon diseased stems developed the disease imme- 

 diately after the union was formed. 



Tests were made to determine the effect of fertilizers, potassium nitrate an<l ammo- 

 nium sulphate being tried. These were applied at the time of seeding and also at the 

 time of transplanting, but no marked effect could be noticed. Observations made to 



