12 



FIELD STUDIES OF THE CROWN-GALL OF THE GRAPE. 



wound tissue, but later in the season they often assume a dark-brown 

 or black color due to the death and decay of the outer tissues. 



OTHER MANIFESTATIONS OF THE DISEASE. 



The disease manifests itself in a number of ways in addition to 

 the formation of galls. The affected vines are stunted in their 

 growth. The leaves are usually smaller and are often etiolated or 

 chlorotic. The galls usually die annually, and if under ground they 

 commonly rot away, the decay killing the adjacent tissues of the 

 root and often killing the vine above the point of attack. 



DEVELOPMENT OF THE FORMS OF CROWN-GALL. 



DEVELOPMENT OF ROOT GALLS. 



The subterranean form of the disease usually does not develop 

 abundantly the first year on vines grown from cuttings. An excep- 

 tion must be made where cuttings are taken from diseased vines. 

 In an experiment with cuttings selected from healthy and diseased 

 vines of the same varieties a marked difference was noted in the 

 relative development of the disease. The experiment was conducted 

 as follows: 



Cuttings were taken from apparently healthy and from plainly dis- 

 eased Thompson Seedless, Zabalkanski, Black Malvoisie, and Mission 

 vines from the same vineyards at Bernalillo and Mesilla Park, N. Mex. 

 They were planted in the greenhouse in sterilized soil in sterilized 

 pots ° and watered with boiled water. The results of the experiment 

 are shown in Table I. 



Table I. — Results of an experiment to determine the relative susceptibility to crown- 

 gall of four varieties of grapes grown in New Mexico, cuttings being made from appar- 

 ently healthy vines and from vines plainly diseased. 



It will be seen from the table that the use of cuttings taken from 

 plainly diseased plants increased the development of the crown-gall 



« Sterilized in an autoclave for three hours at a temperature of 110° C. (230° F.). 

 183 



