178 CROW]Sr-GALL OF PLANTS. 



The results of the inoculations seemed to indicate that the change 

 must be in the plant itself, for the galls that formed from the presence 

 of this newly isolated organism were also slow growing and did not 

 reach half the size of those galls produced when the first daisy plants 

 were inoculated. 



The idea then began to take shape that this failure of the organ- 

 ism to form a gall of the usual size when inoculated into the most 

 favorable growing daisy tissue might be due to some substance 

 developed in the plant for protective purposes, and experiments 

 were planned to determine if daisy plants could be made immune 

 to this disease through repeated inoculations into the same plant or 

 into rooted cuttings made therefrom. 



In the following tests the plants used were taken at their most 

 favorable age — that is, they were inoculated when the tissue was 

 young and tender, so that the organism would have the best possi- 

 ble opportunity to produce the disease. Because cuttings did not 

 grow well in the winter months the work was confined generally to 

 the spring and summer. 



(1) In March, 1907, a dozen daisy plants of the Queen Alexandra 

 variety were inoculated with the daisy gall organism. These plants 

 had never been known to have galls and had not been inoculated 

 before. In two months' time good-sized galls had formed at all 

 the points of inoculation. 



(2) Cuttings (first set) were made from the preceding plants in 

 May, 1907. The cuttings were growing well in July and then a 

 second series of inoculations were made on them. A dozen plants 

 were used this time. Galls formed which were as large as those of 

 the first series. 



(3) In November, 1907, cuttings (second set) were made from the 

 plants of the second series, but they did not grow well at first and 

 it was decided to wait until growth had started up well in the spring 

 before further work was done with them. The inoculations (third 

 inoculations) were made in April, 1908. Galls formed at each inocu- 

 lated place, but they were much smaller and grew very slowly. In 

 August they were less than half the size of the galls of the first series. 



(4) Twenty-five cuttings (third set) were made from these diseased 

 plants on August 17, and inoculations (fourth series of inoculations) 

 were made November 18, 1908, on a dozen plants two and three 

 shoots each. In the meantime a new strain of the Queen Alexandra 

 daisy was purchased from a florist and the virulence of the organism 

 checked up on these new plants which had never been affected with 

 the gall. Large galls formed on the new daisies in a month, but 

 there were none on the third set of cuttings. This was the fourth 

 time that strain had been inoculated. 



213 



