230 JOURNAL OF ECONOMIC ENTOMOLOGY [VoL 3 



the case of the White Magdalen variety that has grown 150 years in 

 Massachusetts without contracting the disease.) 



Since in our work we have to do more work with this disease than 

 the others I shall mention, I shall take a little more time with it and 

 mention some of the points which are in much need of further study, 

 as apparently no extensive scientific work has been done on this im- 

 portant disease for nearly twenty years. 



First. Can the disease be communicated by the pruning knife, 

 contact, etc., or by sap or other non-living matter from diseased trees? 



Second. Can the disease be produced in healthy trees far south of 

 the yellows region by budding from diseased northern stock? Also 

 would young diseased trees recover if transported to the south ? Appar- 

 ently any quantity of trees have been sent south from infected dis- 

 tricts without spread of the disease, though healthy trees from the 

 south have not shown immunity. 



Third. The southern and western limit of the disease should be 

 again accurately determined, and a careful survey of the infected 

 region made to determine if there are within it isolated areas free 

 from the disease. The border line should be completely explored for 

 cases of recovery or recent extension of the disease limitation. 



Fourth. What is the relative resistance of different varieties? Old 

 trees standing for years after the surrounding ones have gone out 

 with yellows should be propagated from to secure possible resistant 

 stock. 



Fifth. Tabulate from orchard inspection and weather records ac- 

 curately kept for many years, the relation of warm, cold, wet and dry 

 seasons and late spring frosts to increase or decrease of yellows in 

 following years. Three or four seasons records in Maryland indicate 

 that yellows outbreaks follow severe cold after buds open in spring. 

 In this connection, the influence of different slopes or exposure and 

 effect of late and early blooming might be considered. 



Sixth. Careful examination of records should be made to cer- 

 tainly determine whether removal decreases infection or spread, bear- 

 ing in mind the possibility that new cases may be due to climatic or 

 soil conditions. 



Seventh. We need a thorough chemical study of the relative amount 

 of organic compounds associated with nutrition such as, starch, sugar, 

 acid, tannin, proteid, enzymes, etc. There are several diseases of other 

 plants closely resembling yellows, such as the Serah disease of sugar 

 cane, dwarf mulberry disease, mosaic disease of tobacco, etc., in which 

 the disturbance has been more definitely worked out, and while it is 

 said that yellows is such an enzyme disease, no chemical study of it 



