236 BACTERIA IN RELATION TO PLANT DISEASES. 



EXPERIMENTS OF 1909 (1908 CONTINUED). 



March 22, ipog. None of the cuttings rooted. None of the peppers or egg-plants have con- 

 tracted the wilt. Probably the stems were too woody when transplanted. The heavily pruned ones 

 recovered very slowly. The older rooted tomatoes gradually got worse and worse, but with no 

 definite wilt, or brown stain in the stems, or bacterial occupation of the vessels. The checks finally 

 contracted the same disease. One of the tobaccos (a large plant now) has contracted the bacterial 

 wilt. Its vessels are full of the gray slime, especially on one side. This was most abundant in the 

 lower part of the stem, but was traced out into the leaves and into the top of the plant just under the 

 seed pods, where a few vessels were browned and occupied by the bacteria, as shown by a microscopic 

 examination. In the middle of the stem the bacterial slime was very abundant, but agar poured- 

 plates sowed copiously showed at the end of the seventh day only intruders (a few colonies with finger- 

 like radiations). The right organism was not recovered with certainty even on a second set of plates 

 made the fifth day from the second dilution tube, which had been kept and was then clouded. The 

 only possible inference is that the parasitic bacteria had been present in this part of the stem for some 

 time and that they were now dead supplanted by saprophytes. The outside of the stem, on one 

 side over the most badly affected part of the vascular cylinder, bore long dark stripes and sunken 

 places. This tobacco was one of those not root-pruned. 



From the interior of a basal branch of the same plant which was then wilting, another set of plates 

 was poured on March 30 and these plates yielded the right organism. 



On May 6, 1909, a second tobacco plant wilted with characteristic signs, and poured plates made 

 from the browned interior yielded the right organism. 



July 6, 1909. The experiments with tobacco, egg-plants, and peppers were closed out to-day 

 with the following results: 



(1) Tobacco: 8 plants healthy, 4 diseased. From 2 of the diseased, as already stated, Bad. solanacearum was plated 



out; the other 2 had similar signs but no cultures were made. 



(2) Egg-plant: There was no definite wilt on these egg-plants during the whole of the time they stood in the bed; 9 of 



them are sound, 2 being in fruit and the rest in blossom; I is wholly rotted, and 2 are gone, i. e., perished 

 earlier. 



(3) Pepper: There has been no indication of wilt in the peppers during the whole time they have stood in the bed. 



Like the egg-plants, the root-pruned ones never fully recovered. There are now 9 free-growing peppers bear- 

 ing green and ripe fruits in abundance and 9 stunted peppers (the root-pruned ones) ; six plants perished ear- 

 lier, but with no definite signs of this disease. There is a trace of brown stain in one or two places in the wood 

 at the base of the stem of 3 of the root-pruned ones, and a microscopic examination shows the presence of 

 tyloses in the browned vessels, but no distinct evidence of bacteria. The bed was now spaded up and prepared 

 for large tomato plants. 



On April 24, 8 good-sized tomato plants were inoculated with the organism plated from the 

 interior of the diseased tobacco on March 30. These inoculations were made from slant agar-cultures 

 of April 21 by means of needle-pricks on the stem, 2 plants being inoculated from each culture, a 

 large amount of material being introduced and 2 internodes of each shoot being pricked. On May 6, 

 six additional plants of the same series were inoculated from a beef-broth culture of April 22 in the 

 same thorough manner. The tomato plants were rapid-growing, rather tall individuals, propagated 

 from cuttings. 



July 6, 1900. The tomato plants continued to grow rapidly and up to this date none of them 

 have ever shown any trace of wilt, with the exception of one plant, which after a time showed one or 

 two slightly wilted leaves that subsequently recovered their turgor. The tomato was a free-bearing, 

 red, small-fruited, hothouse variety. 



Final Note. The organism appears to have died out of the soil which yielded so many 

 diseased plants (tobacco and tomato) in 1908. It was moved to another hothouse and 

 tomato, tobacco, and the Porto Rican spiny weed (p. 182) grown in it for a year, but with 

 wholly negative results. 



In 1912, Coleman, of Mysore, told me he had observed the same thing at Bangalore 

 in connection with his work on the Indian potato-disease. After about 2.5 years an arti- 

 ficially infected soil was no longer infectious. 



This is a highly important matter deserving of thorough study. Very likely the growth 

 of certain soil saprophytes may serve to bring about destruction of Bad. solanacearum in 

 certain soils, and if they could be obtained in pure culture, they might be sown to advantage 

 on infected lands. Since this was written Honing has obtained some evidence bearing on 

 this point (see fig. 134). 



Perhaps, also, a proper course of rotation and cultivation would do much to free the soil. 





