182 CEOWN-GALL OF PLANTS. 



daisy gall by Miss Brown and believed to be the right thing because 

 it behaved tj^pically on agar. The inoculations were made by the 

 senior writer, assisted by Miss Bryan. Five days were devoted to 

 the work, and, as 85 check plants were held, interesting results were 

 anticipated, but no galls ever formed. The check plants (with two 

 exceptions, 1020 and lOSe),*^ also remained free, although they were 

 in a growing condition and derived from plants never before inocu- 

 lated and not long in the hothouse. The experiment must, there- 

 fore, be set down as a lost one without knowing quite why. Prob- 

 ably the failure must be ascribed to the use of a nonvirulent colony. 



The plants stood in 10-inch pots, occupying the whole of a 125-foot, 

 well-lighted greenhouse bench, and made throughout a good growth. 

 They were of two susceptible varieties. 



When the final examination was made in August, 1910, the plants 

 were large and had been in bloom all summer. Occasional shoots 

 showed a slight knobbiness where the needle pricks entered, and often 

 there was more than the usual amount of corkiness in the pricked 

 areas, but not a single tumor resulted from the inoculations. That 

 these plants were still subject to infection (given a sufficiently viru- 

 lent organism) is indicated by the fact that 13 of them bore natural 

 tumors on the stem at the surface of the earth. Six of these tumors 

 were large; the others were less than 1 inch in diameter. The par- 

 ents of all of these plants (about 21 large daisies) all bore similar 

 natural (and large) tumors on the base of the stem at the time the 

 cuttings were made, and, as already stated, the plants from which 

 they in turn were propagated had been (they or their progenitors) 

 several times artificially inoculated with the production of galls. 

 Cuttings were now made (August 5, 1910) from a large number of 

 these plants for a second large experiment, and cultures were plated 

 from the most favorable looking (youngest) of the 13 knots, with a 

 view to obtaining a more virulent strain with which to make subse- 

 quent inoculations. 



In November, December, and January inoculations were made on 

 these plants as follows : 



(1) With subcultures from a colony on a plate poured from the 

 most favorable of the 13 tumors just mentioned. 



(2) With subcultures from a colony on a plate poured from a daisy 

 tumor occurring on a "nonresistant" plant. 



Both these sets failed to produce tumors. Not only was this true 

 of the "resistant" plants, but also of the check plants never before 

 inoculated. 



(3) Isolations were now made from a gall growing on one of Miss 

 Brown's resistant plants (sixth series), and subcultures from two of 



o These had very small galls In the inoculated places at the end of a year. 

 213 



