2 BULLETIN 957, U. S. DEPARTMENT OF AGRICULTURE. 
No attempt has ever been made to collate and summarize the 
results of all the experimental 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. R. 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. L, 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The writer thanks the following people for unpublished data which 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 
