2 BULLETIISr 957, U. S. DEPAETMENT OF AGRICULTURE. 



No attempt has ever been made to collate and summarize the 

 results of all the experunental work. The mass of information is so 

 large and so scattered that it is nearly impossible for a single indi- 

 vidual, even now, to learn what has been done. This condition is 

 certain to become more and more acute as the extensive and intensive 

 researches now under way progress. Various States are taking up 

 work on this disease, and the multiplication of workers can only 

 result in confusion and unnecessary duplication of work unless the 

 ascertained data are arranged and made available for all. This 

 bulletin aims to present the available information so that the gaps 

 in our knowledge may be readily perceived and new investigations 

 planned to the best advantage. 



The work of the Office of Investigations in Forest Pathology has 

 been conducted under the direction and advice of the writer by the 

 following persons: In 1915, G. F. Gravatt and Dr. G. R. Lyman; 

 in 1916, Dr. E. H. Colley, G. F. Gravatt, and Miss M. W. Taylor; 

 in 1917, Dr. R. H. Colley, G. B. Posey, G. F. Gravatt, Rush P. Mar- 

 shall, and Miss M. W. Taylor; in 1918, Drs. R. H. Colley, H. H. York, 

 L. H. Pennington, L. O. Overholts, A. S. Rhoads, T. C. Merrill, 

 W. H. Snell, D. M. Benedict, and Miss M. W. Taylor; in 1919, Drs. 

 R. H. Colley, H. H. York, and L. H. Pennington, D. M. Benedict, 

 J. E. Lodewick, W. H. Snell, P. R. Gast, Miss A. E. Rathbun, and 

 Miss M. W. Taylor. Dr. G. G. Hedgcock made a comparative study 

 of Cronartium occidentale and C. ribicola on Ribes on Block Island, 

 R. I., in 1919. 



The work of Dr. L. H. Pennington, D. M. Benedict, and J. E. Lode- 

 wick, in 1919, was maintained in formal cooperation with the New 

 York State College of Forestry at Syracuse University. 



The endeavor has been to show plainly in this bulletin who did 

 each piece of work without entering into details to an objectionable 

 extent. 



The writer thanks the following people for unpublished data which 

 have been placed at his disposal: Mr. W. A. McCubbin, formerly of 

 Canada; Dr. Ed. Fischer, of Switzerland; Dr. A. B. Borthwick, of 

 Scotland; Mr. A. D. Cotton, of Kew Gardens, England; Prof. L. 

 Mangin, Museum of Natural History, Paris; Prof. F. K0lpin Ravn 

 and Mr. J. Lind, of Denmark; Dr. L. O. Kunkel and Mr. W. Stuart 

 Moir. of this country. 



The writer and his collaborators are indebted for material for 

 experimental use to the Arnold Arboretum of Harvard University; 

 the Dominion of Canada Central Experimental Farms; the Park 

 Board of Rochester, N. Y.; the Conservation Commission of the 

 State of New York; the Office of Horticultural and Pomological In- 

 vestigations and the Forest Service, of the United States Department 

 of Agriculture. The Office of Blister-Rust Control has contributed 



