248 BACTERIA IN RELATION TO PLANT DISEASES. 



Up to this time the evidence in favor of the oneness of the squash-disease and cucumber- 

 disease rested on the following facts : 



(i) One case of the wilt disease in cucumber obtained by inoculating /owr plants with 

 the milky bacterial ooze taken directlyfrom the interiorof a diseased squash-stem (September 

 I, 1894). 



(2) Primary wilt on several squash-leaves inoculated November 17, 1894, with a pure 

 culture obtained from a cucumber. 



(3) The rather inconclusive evidence afforded by the presence of bacilli in some of the 

 vessels of plant No. 79, examined 2| months after inoculation, fungi being present also in 

 some parts of the stem. 



Opposed to this were many failures to convey the disease by needle-pricks using pure 

 and virulent cultures of the bacillus. In my experiments on these squashes some unknown 

 conditions necessary to infection were not fulfilled. In nature the squash takes the disease 

 readily enough although it succumbs to it much less easily than the cucumber. That the 

 disease is inoculable from squash to squash was also established by my experiments in 

 Michigan in September, 1893. Whether the squash would contract the disease in the field 

 as readily from melons and cucumbers as from squashes, remained to be determined. 



Inoculations of March 18, 1895. 



In the hothouse 24 tomato-vines and 6 Japanese pear-seedlings were inoculated with 

 bacteria from a white, wet-shining, thin, sticky, motile growth on slant agar (tube No. 3, 

 March 13, from stab No. 4, January 9. The culture in great part was much younger than 

 March 13, the uninoculated surface of the slant having been spread over with bacteria 

 from the other parts on March 16). Each plant was given a dozen or more pricks. The 

 bacteria were lifted on a sterilized cooled needle. The inoculations were begun about 10 

 a. m. and finished at 4.30 p. m. It was a windy drying day with a hot sun under the glass. 

 The tube was carefully shielded from all but very short exposures to direct sunlight. 

 Thousands of living bacilli were pricked into each plant. The needle and loop were flamed 

 before each set of inoculations and not used till cool. As an additional precaution the needle 

 was always thrust first once or twice into the cool stem and then used. A loop of the white 

 slime was put on the surface of the stem and stabbed in repeatedly. An examination of 

 each one of the inoculated plants was made on March 27, April 15, May 9, and later dates. 



(117.) Tomato (Lycopersicum esculentum) . A thrifty vine about 30 inches high was pricked at 

 the base of one of the upper branches (two nodes and the internode). The tissue was rather firm. 



There was no result (May 9). 



(118.) Tomato (same plant). Two internodes and one node near the tender apex of a basal 

 shoot. The tissues were soft and the needle entered very easily. 



There was no result. By May 9 the shoot had grown 2 feet since it was pricked. 



(119.) Tomato. A thrifty vine about 25 inches high was pricked in a node and two internodes 

 in the apical part of a branch. The tissues were immature and tender. 



Between the time of inoculation and May 9 the pricked branch grew over 18 inches. There was 

 no result from the introduction of the bacteria. 



(120 to 140.) Tomatoes of the same size and inoculated in the same way as the preceding. 



No disease resulted. The 2 1 plants were under observation for 52 days. 



(141.) Japan Pear Seedling {Pirus sp.). Pricks were made in the growing tip of a shoot. 



There was no result. 



(142 to 146.) Five Japan Pear Seedlings. lyikeNo. 141. 



No result. 



Remarks. — None of the tomato-shoots or pear-shoots showed anything but slight local 

 disturbances as a result of the inoculations. The pear-shoots blackened around the needle- 

 punctures almost immediately (host reaction) and after that showed no change. The toma- 

 toes swelled slightly around the pricks in some cases, and in others there was a slight falling 

 in and discoloration of tissue immediately surrounding the needle-pricks, nothing more. 



