REPORT OF THE SECRETARY. 55 



nursery disease. Yet this appears to be the case. The white-pine 

 blister rust, referred to in previous reports, is unquestionabl}^ still 

 being imported. xVll importations that could be located have been 

 inspected and all visibly diseased trees destroyed, but there are no 

 means of locating all importations. The importation of white-pine 

 seedlings should be flatly prohibited, as the damage which this dis- 

 ease can do, and probably will do, if once established in America, is 

 out of all proportion to the value of all white-pine seedlings ever 

 imported or ever likely to be. 



Data collected in the forest-disease survey have indicated that in 

 America timber decay and tree disease are second only to forest fires 

 as causes of loss. In theory it is easy to remove diseased trees in 

 the forest when cuttings are made, leaving only healthy individuals 

 for seed trees, and so continually improve the health of the forest; 

 but in practice so many questions of economy and differing local 

 conditions are involved that many difficulties must be overcome. 

 The Bureau of Plant Industry has given a great deal of attention 

 to working out this problem, in active cooperation with the Forest 

 Service. To this end, pathologists have been stationed in four of 

 the six Xational Forest Districts. In District 5 great progress has been 

 made in so conducting timber sales that all dangerously diseased 

 trees are removed and only healthy and desirable individuals are 

 left to propagate the future forest. Probably the most important 

 function of these " district pathologists " is to look out for dangerous 

 new diseases. There is every reason to believe that if the chestnut- 

 bark disease, for example, had started in a National Forest District 

 having a pathologist it would have been eradicated as a matter of 

 routine before infection became general. Great epidemics of this 

 kind are as serious in their effects as forest fires, and there is no 

 reason why as strenuous efforts should not be made to control them. 



CROWN-GALL AND OTHER PLANT DISEASES. 



An important line of work carried on during the past year has 

 been a continuation of the study of crown-gall of plants, with special 

 reference to its relation to malignant animal tumors. The new facts 

 we have learned are, in brief: (1) That bacteria occur also in the 

 secondary tumors; (2) that in most cases the secondary tumors are 

 connected with the primary tumor by a deep-seated strand of tumor 

 tissue, from which the original bacterium has been cultivated out; 

 (3) that the cell structure of the secondary tumor is like that of the 

 primary tumor, e. g., when the primary tumor occurs on the stem 

 and secondar}'^ tumors subsequently appear in the leaves the struc- 

 ture of the leaf tumors is that of the stem. A bulletin is in prepara- 

 tion which will fullv illustrate these new features. 



