THE QUESTION OF IMMUNITY, 179 



At the end of a month (December 22, 1908), as there was no trace 

 of a gall starting to form, the same 12 plants were inoculated again 

 (fifth series of inoculations) further to test the case. These plants 

 were watched carefully but no galls formed. In a few cases the 

 tissue at the points of inoculation was raised a Httle as though the 

 presence of the organism had had some little effect. As galls formed 

 at every point of inoculation on the check plants the organism used 

 for the inoculations was proved to be all right. However, four months 

 after this last inoculation of the third set of cuttings, the plants were 

 examined again, and a gall was found on the root of one of them and 

 one on the stem of another where a cutting had been taken. 



(5) In March, 1909, cuttings (the fourth set) were made from the 

 plants W'hich seemed to be immune, and on May 20 they were inocu- 

 lated as follows (sixth scries of inoculations), some with the daisy 

 organism wdiich had been used through the entire test (strain B), 

 some with the peach-gall organism, and some with a daisy organism 

 recently plated from a gall and proved up by other inoculations. 

 Six to 8 shoots on each of 6 plants were inoculated with the old-daisy 

 organism; 4 plants including a like number of shoots on each were 

 inoculated wath cultures of the crown-gall of peach organism; and 6 

 plants with cultures of the daisy-gall organism recently plated out. 

 In all there were over a hundred inoculations, i. e., groups of punctures. 



There were no daisy plants available for controls, so young sugar- 

 beet plants about 6 inches tall were inoculated at the crown with the 

 same cultures. Two beets w^ere inoculated with cultures of the old 

 daisy, 2 with the new daisy, and 2 wdth the crown-gall of peach organ- 

 ism. Sugar beets were used because they had been found to take 

 the gall very readily. 



On June 18, 1909, there was not a trace of gall formation on any 

 of the daisy plants inoculated May 20. The checks of the peach gall 

 and of the old daisy (both on the sugar beets) had good-sized galls, 

 but those beets inoculated with the new daisy had none. These 

 plants, however, were in a shady place and had not made much 

 growth since the time of inoculation. The galls on the 4 sugar 

 beets were accounted sufficient proof that 2 of the 3 strains were 

 able to produce galls in susceptible plants. 



The same day (June 18, 1909) some of the same daisy plants were 

 inoculated again with the crowTi-gall of peach organism, 16 groups of 

 punctures being made (seventh inoculation). The plants were 

 growing very well. Five young sugar beets were inoculated at the 

 crown with the same cultures as checks on the daisies. 



On July 6, 1909, the plants w^ere examined and no galls were found 

 on the daisies; 2 of the 5 sugar beets had small galls which bade fair 

 to increase in size as the beets grew. 



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