182 



BACTERIA IN RELATION TO PLANT DISEASES. 



merits were not very numerous, and, especially, were not very long-continued. Basing our 

 conclusions on Hunger's experiments with tomato roots, we may assert with some degree of 

 confidence that an unwounded root is impervious to this organism, but it does not appear to 

 be equally certain that the disease can never begin in the sub-stomatal chamber. So far, 

 however, as we yet know definitely, infection takes place only through wounds. In one of 

 the writer's hothouse experiments, a potato plant grew to maturity in health in the same pot 

 with one which became badly diseased (in leaves, stems, and tubers) as the result of a pure- 

 culture inoculation, but here insects were kept off. 



Exclusive of variable degrees of virulence on the part of the parasite and of individual 

 or varietal resistance on the part of the host, the progress of the disease on attacked plants 

 in the field must vary to a large extent with fluctuating temperature and rainfall. Rainy 

 weather favors the disease, beyond 

 question. So does moist soil. Under 

 the equator, with rain every day, one 

 might expect the disease to be much 

 more rapidly fatal than in a cooler, 

 drier climate, and such appears to be 

 the case. 



According to Mr. Irons, of Porto 

 Rico, Solatium mammosum is resistant 

 to this disease. The Seed and Plant 

 Introduction No. 24650, supposed to 

 be this plant, bears small yellow 

 gourd-like fruits having a white, 

 tough, inedible flesh and small brown 

 seeds. The specimen fruit seen by 

 the writer was globose and about 2 

 inches in diameter. It is thought 

 that the egg-plant and tomato might 

 be grafted upon it, but I believe we 

 shall find eventually more practical 

 methods of dealing with this disease. 



SYNOPSIS OF INOCULATIONS. 



The following is a summary of all 

 inoculations made by the writer and 

 his assistants with Bacterium solana- 

 cearum, so far as records were kept 

 and are now available, except certain 

 ones mentioned under "Wilt Diseases 

 of Tobacco:" 



Fig. 88.* 



May -?", t8qS- Tomato and potato plants were inoculated with slant agar culture No. 2 of May .?-' 1 from slant agar, 

 May 16, which was direct from the interior of a green, turgid, odorless stem of tomato from Ocean Springs, 

 Mississippi). Fourteen inoculations were made: In fruit, rather woody part of stem, tip of stem, leases 

 and petioles of tomato, and on young shoots and leaflets of potato. 



*FlG. 88. Cross section of a single bundle from the hypocotylof Datura stramonium, plant No. 23, inoculated June 

 8, 1895, from tulie 1, June .), with Bacterium solanacearum by needle-pricks on hypocotyl and fixed in strong alcohol 

 on June 20. The upper part of tin- drawing represents the outer part of the bundle. In the lower part there is a bac- 

 terial cavity. In the lower left corner the knife passed through a crystal-cell. A few nuclei are visible. The alcohol 

 caused some shrinkage of tin- bacterial masses. Several other bundles of this hypocotyl are partially occupied; the 

 remaining bund! tb 1 with the tissues between them and on the periphery, are free from bacteria. Thefoliageof 



this small plant was badly collapsed when the material was cut for fixing. Drawn by Alice C. Haskins under the Abbe 

 hi. Slide 192(1. The organism inoculated was a culture from a tomato plant from Ocean 

 Springs, Mississippi. 



