120 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



largely confined to the study of the bacterial organism which is the cause 

 of the disease. 



It was found early in the work that the problem was much broader 

 than one simply of bacteriology or plant pathology proper, and as the 

 investigation developed, it became necessary to study the whole sub- 

 ject of walnut culture from a horticultural or pomological standpoint. 

 The establishment of the Southern California Plant Disease Laboratory 

 at Whittier as a permanent institution made such work possible. Soon 

 after the location of this laboratory, space was obtained on the grounds 

 of the Whittier State School for orchard planting of walnuts. Upon 

 this ground there was commenced, in the spring of 1907, an experi- 

 mental walnut orchard, in which may now be seen representative trees 

 of all the important varieties. Upon the same grounds, and also those 

 of the laboratory proper, a large amount of nursery work was also 

 commenced in connection with the study of methods of propagation 

 of the walnut, testing of different roots and other similar subjects. 

 In 1909 this portion of the work was mostly transferred to the Pasa- 

 dena City Farm near Alhambra, where it could be carried out on a 

 much larger scale. In addition to nursery experiments, considerable 

 work has also been done in the vicinity of Whittier and in other places 

 in top-grafting walnut trees in the orchard with the idea of determin- 

 ing the feasibility of working over undesirable trees to better varieties. 

 Much work has been done in searching for desirable walnut trees all 

 over the State, and such trees when found have been tested out quite 

 extensively by propagation, both in the nursery and upon old trees, as 

 mentioned above. A large amount of top-working of this sort has been 

 done upon the Pasadena City Farm, where a large seedling walnut 

 orchard already existed, and also in conjunction with several growers 

 in various parts of the State. Scions and nursery trees of promising 

 varieties have also been distributed quite extensively during the past 

 three or four years. In this way many new varieties will be tested in 

 various parts of the State much more quickly than would otherwise 

 have been the case. Considerable testing of root stocks has also been 

 brought about by the same means. A line of work similar to that at 

 Whittier has also been inaugurated on the University Farm at Davis, 

 and it is hoped that this work may be continued and extended there 

 on account of the growing importance of the walnut industry in the 

 northern part of the State. As now presented, the results of this inves- 

 tigation cover practically all phases of the subject of walnut culture in 

 California, both north and south. 



The English or Persian walnut, Juglans regia, constitutes one of the 

 most important and one of the most attractive tree crops of California. 

 In southern California, to which portion of the State the crop on a 



