EFFECT OF CROWN-GALL ON THE PLANT. 177 



a greater extent than apples, and roses in hothouse culture are still 

 more conspicuous examples of it. Unfruitfulness has also been 

 observed in the last three species and in the grape. A large part of 

 this phenomenon is perhaps attributable to simple abstraction of 

 food and water. In case of the daisy this often proceeds to such an 

 extent that individual branches projecting beyond well-developed 

 galls present a starved appearance and die prematurely. 



This disease never induces premature development of blossoms 

 and fruit so far as observed, but on the contrary retards develop- 

 ment — rose, daisy, apple. 



It is a difficult matter to determine whether the substances elabo- 

 rated in the tumors by the parasite or by the saprophytes wliich 

 follow it are absorbed and act as slow poisons on the remoter tissues, 

 but there is some warrant in the appearance of the plants for this 

 assumption. 



Death of galled cuttings may occur within a few months, but ordi- 

 narily on well-rooted plants it either does not occur at all — i. e., the 

 the plant outgrows the disease — or it occurs only after a lingering 

 illness of many months or several years, and then frequently as the 

 result of secondary infections due to other organisms. 



In many of our inoculated daisies we have observed what we have 

 interpreted as increased resistance due to the long-continued growth 

 of tumors on the plants, and consequently there would appear to be 

 reactions set up in the plant which are possibly comparable with 

 some of those observed in the animal body. We do not yet know 

 to what substance this increased resistance is attributable. The sub- 

 ject is dealt with more fully in the following chapter. 



EXPERIMENTS SHOWING INCREASED RESISTANCE OF THE HOST 

 DUE TO REPEATED INOCULATIONS AND ALSO DECREASED 

 VIRULENCE OF THE BACTERIA. 



While the work with the different gall organisms was being car- 

 ried on extensively, a group of plants of the Queen Alexandra daisy 

 or progeny of the same was used constantly for inoculating, and the 

 dimmishing size of the galls that formed in comparison with those 

 of the first inoculations and also the longer period of time required 

 for their formation drew attention to the fact that either the organ- 

 isms used were less virulent than when they were first isolated or 

 else that a change was taking place in the plants themselves. To 

 determine which hypothesis was the correct one fresh daisy gaUs 

 were taken and the organism plated out to get a strain which had 

 not become attenuated through repeated transfers on culture media. 

 The new strain was inoculated into cuttings made from galled plants 

 which themselves had been cuttings from previous gaUed ones. 

 78026°— Bull. 213—11 12 



