2 
BULLETIN 1156, U. S. DEPARTMENT OF AGRICULTURE. 
infested area showed that susceptible potatoes predominated. 
Subsequent tests of a large number of tuber selections among the 
diverse types grown in this area confirmed the fact of the general 
culture of susceptible types. The bearing of this upon the restricted 
distribution of potato wart in the United States, as brought to 
light by the disease survey (Fig. 1), is of particular importance, 
for it is believed that shipments of potatoes equally capable of 
introducing the parasite as those which found their way into the 
mining towns of Pennsylvania may have reached diverse sections 
of the country, but failed to introduce the disease because of the 
prevalent culture of immune varieties in many sections. 
Fig. 1. — Outline map of Maryland, Pennsylvania, and West Virginia, showing the geographical distribu- 
tion of potato wart on September 1, 1922*. Localities of findings: 1, Original eastern Pennsylvamaarea: 
2, Nanty Glo; 3, Whitmer; 4, Thomas; 5. Lilly; 6, Llanfair: 7, Vintondale; 8, Osceola Mills; 9, Clarence; 
10, Woodvale; 11, Robertsdale; 12, Smithmill; 13. Mount Savage, Eckhart Mines, and Lord; 14, Midland; 
Charles Town, and Detmold; 15, Yatesboro; 16, Beaverdale: 17, Onnalinda. (Prepared by the Office of 
Plant-Disease Survey, Bureau of Plant Industry.) 
It became necessary, therefore, to prohibit at once the cultiva- 
tion of potatoes in all gardens which were known to be infested, 
but it was thought desirable to permit the continued use of sus- 
ceptible varieties in the general area, in order to determine the 
ultimate extent of infestation; meantime, the rest of the country 
was protected against extension of the disease by a quarantine 
on the movement of potatoes and materials capable of transporting 
the parasite from the infested area as then known. 
The lateness of the season when wart was discovered prevented 
making tests of varietal susceptibility in 1918, but during the winter 
it was determined that the Triumph variety was susceptible. The 
