180 CEOWN-GALL OF PLANTS. 



This last set of cuttings (fourth set) in which two sets of inocula- 

 tions had been made already was subjected to one more test. A 

 fresh strain of the peach-gall organism which had been isolated in 

 April, 1909, from some trees grown in Virginia was used for these 

 inoculations. This organism was selected because it had produced 

 galls very rapidly on a daisy plant which had never been affected 

 with this disease. In July, 1909, 43 inoculations (eighth series of 

 inoculations) were made. Five young sugar beets were inoculated at 

 the crown with the same cultures used on the daisies. On August 

 30 the last inoculations of the daisy were examined and no trace of a 

 gall was found on any. Of the 5 sugar beets only 1 had a gall; the 

 beets had grown scarcely at all since they were inoculated, so they 

 were repotted and left to develop. October 4: These beets never 

 grew to any extent, but 1 other bore a tiny gall. 



On September 20 all of the plants included in the fourth series of 

 cuttmgs were taken from the pots; the soil was washed from the roots, 

 after which they were examined thoroughly. Four out of the 16 

 plants had galls on the roots, only 1 of which was of any appreciable 

 size. 



(6) Cuttings were again made, this being the fifth set from the 

 original galled plant. For checks, new daisy plants of the Queen 

 Alexandra variety were purchased from a Boston firm and grown 

 under the same conditions, so that both sets of plants would be about 

 the same age when inoculated. 



A fresh strain of the daisy organism was obtained in November, 

 1909, by plating from a gall, and inoculations were made December 1 

 on 31 of the supposedly resistant cuttings which were growing 

 well and on 16 of the new daisies from Boston never before inoculated 

 to be held as checks. The first subcultures from the poured plate 

 colonies were used for the inoculations. 



On December 14 (two weeks' time) galls had formed on 14 out of 

 the 16 daisies of the new strain, but none whatever on the resistant 

 strain. 



On December 21 a gall had formed in one of the resistant cuttings; 

 it was very tinv, but unmistakably a gall. By this time (end of 

 third week) galls had formed on all the check plants and were from 

 half an inch to an inch in diameter. 



On January 6, 1910, 14^ out of the 31 resistant cuttings had small 

 galls starting to form. Some of these were merely a slight swelling. 

 This was thirty-seven da3^s after inoculating, and it will be remem- 

 bered that all but 2 of the check plants had galls within two weeks. 



On January 18 (forty-nine days) the supposed resistant cuttings 

 were examined again and 23 of the 31 foimd with galls. None of the 

 galls were larger than a small i)ea, however. 



213 



