BROWN ROT OF SOLANACHAE. 213 



capable of causing the disease. These experiments were carried out as follows : The bacteria were 

 removed from diseased potatoes and grown in the laboratory in such a way that they could be sepa- 

 rated from all other forms of bacteria. When by careful testing it was found that we had masses of 

 these bacteria growing cjuite free from any other form, such masses were used to give the disease to 

 healthy potato plants. Small pricks were made in the leaves and leaf -stalks of healthy plants with a 

 fine needle which had been held in a flame to kill off all bacteria that might be on it. Then masses of 

 these bacteria were stroked over these pricks so that the bacteria could enter into the substance of the 

 plant. After a few days it was noticed that the leaves and plants infected began to wilt and in the 

 course of 2 to 4 weeks the plants were quite dead. Moreover, when the stems of these plants were cut 

 across and examined under the microscope these same bacteria were found inside the vessels. Some 

 of the tubers attached to these plants also showed the characteristic brown ring. We have thus 

 shown clearly that these bacteria are the real cause of the ring disease of potatoes." 



Dr. Coleman states that there are at least two common ways of infection as determined 

 by his experiments: (1) Through the planting of seed-tubers which already have the dis- 

 ease, and (2) the presence of these bacteria in the soil of the plot where the potatoes are 

 planted. An experiment was also conducted which showed that potatoes harvested from a 

 plot where the disease was present, even though they did not show the brown ring, would 

 produce the disease if planted in soil unquestionably free from the bacteria the young 

 plants wilting throughout the plot soon after coming up. 



A similar, if not identical, disease is found attacking the potato in America. Dr. Erwin F. Smith 

 of the Agricultural Department, Washington, has studied it thoroughly and has come to the conclu- 

 sion that insects have a great deal to do with the spread of the disease. 



In all my experiments I have kept a very careful watch for any instance of the spread of the dis- 

 ease by insects. * * * On the whole, however, insect attack has been insignificant, and although 

 I have examined very many wilted plants indeed, I have never yet seen one in which the infection 

 could, with any likelihood, be traced to the gnawing of insects. 



Dr. Coleman states that because in case of the above-mentioned potato-disease in Amer- 

 ica Dr. Erwin F. Smith has found that it also attacks egg-plants (brinjals) and tomatoes, 

 he instituted experiments to ascertain whether tomatoes and brinjals can be given the 

 disease. The results already obtained show that both these plants can be infected with it 

 by means of inoculation with pure growths of bacteria, or with bacteria taken direct from 

 diseased potato-tubers. In one successful experiment with tomato-plants, 8 comparatively 

 young plants were inoculated with pure growths of the bacteria; all the 8 contracted the dis- 

 ease and within 3 weeks were practically dead. Three larger plants (bearing fruit) inocu- 

 lated at the same time with the same growths of bacteria remained practically unaffected 

 and could not after 3 weeks be distinguished from an uninoculated plant of the same age 

 (see last paragraph on p. 179). Similar results have been obtained with brinjal plants the 

 younger plants contracting the disease, whereas larger plants resisted it. 



From the results obtained the following directions should be strictly adhered to, if 

 possible : (1) Only such potatoes should be used for seed as have been grown on a plot which 

 has been quite free from the disease; (2) where the seed is cut before planting, all pieces that 

 have the least trace of brown spots or a brown ring should be discarded; (3) if the disease has 

 been prevalent on a certain piece of ground, potatoes should not be again planted there for 

 at least one year. Probably two years would be better, but a definite statement in this con- 

 nection can not be made until the experiments in progress have been completed. Also, 

 brinjals and tomatoes should not be planted on such infected ground. 



Spraying the plants with a fungicidal or insecticidal spray is a waste of both time and 

 money, as the disease is not transmitted, at least to any appreciable extent, by insects; nor 

 can it be carried through the air from plant to plant. Another and a very effective means 

 of checking the disease would be by the introduction of a disease-resistant variety of potato. 

 Experiments in this direction are in progress. 



The description of the organism is withheld by Dr. Coleman for a separate paper. 



