586 Third European Journey 



interesting conclusions, all building to the final point that "Appar- 

 ently the acid produced by Bacterimn tumejaclens is locked up in 

 the tumors nearly or quite as fast as it is produced, but it may 

 nevertheless be the active agent in inciting the cells to abnormal 

 division." More than 250 potentiometer tests of juices from 

 normal and diseased tissues of sunflower, sugar beet, and other 

 plants, had been made, and most of the tumors studied varied in 

 age from three to six weeks, thorough tests of the youngest 

 tumors and the youngest, outermost parts of older tumors not 

 being included. " The general trend of the experiments," he 

 suggested, " indicates that the apical, actively-growing parts of a 

 normal vegetative plant, especially Helianthus annuus, are more 

 alkaline than the middle or lower parts where growth is less 

 active." From sugar beet, comparisons were drawn between the 

 juice alkalinity of youngest and full-grown leaves, and between 

 the juice alkalinity of blades of full-grown leaves and their 

 petioles. In general, the tumor juice, especially for sugar beet, 

 was found to be " more alkaline than the juice of corresponding 

 normal parts, and the older the tumors, up to a certain stage, 

 i. e. until secondary invasions have set in, the more alkaline " was 

 found " their juice — with some few exceptions." Electrometric 

 titrations followed the determinations of pH, and further inves- 

 tigations were promised to decide " whether the tumor juice is 

 ever more acid than the normal juice, as we believed," said Smith, 

 " would prove to be the case when we began these experiments. 

 ... It seems to be so in some instances. It is less alkaline in early 

 stages of growth and in a few instances it has been more acid 

 than normal juice and in other instances it has been of the same 

 pH value, but such readings have not been very numerous." Smith 

 illustrated his paper with twenty-two lantern slides which showed 

 some of the results of their fifteen months of work. 



Immediately on returning to Washington, he and his co-workers 

 continued potentiometer tests of crown galls on sugar beet and 

 sunflower, and on May 2 he started study of "' galled Ricinus 

 plants inoculated April 9th." By June 6 the work included 

 " crowngall on Cauliflower. Doubtful," however, he said, " if pH 

 can be determined electrically. Something seems to interfere." 

 Crown galls on other plants were tested. But not until mid- 

 summer did his diary contain any important memorandum of 

 conclusions. July 31 he wrote: 



