BROWN ROT OF SOLANACEAE. I 79 



cessful in hot wet weather than in cool dry weather, and with cultures recently plated from 

 diseased plants sent in from various parts of the United States than with organisms which 

 have been longer removed from the plant, i. e., cultivated in the laboratory on various nutri- 

 ent media for 6 months or a year. One of two inferences seems to be warranted: (i) the 

 hosts vary enormously from plant to plant and time to time, or condition to condition, in 

 their ability to resist this disease; or (2) the organism readily loses its virulence, for reasons 

 yet unknown, when subjected to ordinary cultural conditions. Both inferences may be 

 true. The subject requires for its elucidation more time than the writer has been able to 

 devote to it. That the failures noted were due to accidental substitution of similar-looking 

 non-infectious organisms was sought as a first explanation and might answer for a single 

 failure, but hardly, one would think, for repeated failures, since the same care was exercised 

 as in the case of other organisms where no such phenomena appeared. Descendants of the 

 most virulent strain the writer ever had in the laboratory (vol. I, pi. 26) lost all infectious 

 power in the course of a year, although apparently preserving the same cultural peculiarities. 

 This strain was isolated from the plant photographed on plate 30. 



When virulent cultures are used on susceptible plants the time elapsing between the 

 puncture and the first appearance of the disease is usually not more than 8 to 10 days and is 

 sometimes as short as 2 or 3 days on watery shoots in very hot weather. All of the success- 

 ful inoculations of 1895 were made with the organism taken from tomato plants grown in 

 Mississippi. The very successful inoculations of 1896 were made with cultures derived from 

 an egg-plant grown at Charleston, South Carolina. In both years infections were obtained 

 on tomatoes and potatoes, the resultant disease being identical with that observed in the 

 field. The organism was demonstrated in the vessels of the plants in enormous numbers at 

 long distances from the points of inoculation (fig. 86, about 15 inches, time 18 days; fig. 82, 

 about 3 feet, time 42 days). Pure cultures were isolated from the interior of such plants 

 and the disease was again produced by means of these cultures. Needle-punctures on leaf- 

 lets of potato produced the disease as readily as those into the stems, the only difference 

 being that the organism had a longer distance to travel and consequently the tubers were 

 not reached and destroyed so quickly. 



Sometimes the organism was observed to pass out into the under portion of the midrib 

 of the potato leaf, blackening it for a distance of several inches in advance of the staining of 

 the upper surface or the wilting of the foliage ; at other times it ran out in long, narrow black 

 lines on the upper surface of the leaf. The most rapid downward movement of the bac- 

 teria in inoculated potato stems was observed during hot weather in July 1896: In 16 days 

 from the date of an inoculation by needle-pricks on the upper part of a stem the bacteria had 

 passed downward a distance of rather more than 2 feet and caused signs of wilt in another 

 stem from the same root. In another tall shoot pricked lower down, i. e., in the more woody 

 tissues 6 inches from the earth, the signs on other shoots from the same root were slower to 

 appear, i. e., they did not develop until after the twentieth day. Signs of the disease were 

 observed to pass up and down stems on the pricked side much faster than sidewise. 



In 1895 a tomato plant which was of large size when inoculated showed local signs after 

 a few weeks, but general signs developed only after a long time. On then making sections, 

 the bacteria were found in the vascular system in enormous numbers and at long distances 

 from the point of inoculation. A similar case occurred in 1903, another in 1905, and still 

 another in 1909. The latter was 12 feet high and full of fruit when it finally wilted. It was 

 inoculated on a terminal shoot when about 4 feet high. It grew well for 3 months after 

 inoculation, showing at first only a feeble wilt of a few leaves, from which it soon recovered. 

 When dissected the upper 6 feet of the stem was free from bacteria. They were very abun- 

 dant, however, in the vascular bundles of the lower 6 feet of the stem, including some of the 

 roots. Cavities had formed in the tissues only near the point of inoculation. The stem 

 was sound externally. The wood was stained brown in the part occupied by the bacteria. 



