2 BULLETIN 1239, U. S. DEPARTMENT OF AGRICULTURE. 
solution and duration of immersion of the seed were largely guess- 
work, particularly where copper sulphate was used and in those 
sections where the smut losses were heaviest. Years of experience, 
however, had convinced the growers that copper sulphate gave 
them better results than formaldehyde, and it finally developed 
that there was good reason for this view. 
THE PROBLEM qF SOIL INFESTATION. 
The writers faced a condition rather than a theory. The seed 
treatments used in the course of these investigations were designed 
principally to confirm the inevitable conclusion that there was soil 
infestation from some source. The question as to the source of 
this infestation then arose. Two possible answers to this question 
presented themselves: 
(1) That this infestation originated in bunted heads left in immense num- 
bers on the ground at harvest time. These bunted heads were found 
to contain viable ungerminated spores after lying in the fields for a year. 
(2) That it was caused by wind-disseminated spores. 
Considered in the light of the investigations of Brefeld and others, 
the first explanation appeared for a time to be the more tenable. 
On the other hand, the experiments herein and elsewhere recorded 
give greater weight to the second explanation. 
The wheat section in which these conditions prevailed is situated 
in the Columbia and Snake River basins of the Pacific Northwest, 
extending from the foothills of the Cascade Mountains on the west 
to the foothills of the Bitter Root Mountains on the east and includ- 
ing the plateau of the Nez Perce and Camas prairies. It extends 
from near the Canadian border on the north to the Blue Mountains 
of Oregon and Washington on the south. 
As a general rule the intensity of the disease increases within this 
area as one follows the course of the prevailing southwest winds. 
Thus, the heaviest losses occur in the Palouse district centering 
about Pullman, Wash., and Moscow, Idaho, and in the high Nez 
Perce and Camas plateaus lying to the east and southeast of Lewis- 
ton, Idaho. Within this general area the altitude ranges from 
about 500 feet near the Columbia River to 2,600 feet at Pullman 
and 4,000 feet in the Nez Perce district. The annual rainfall within 
the area of possible wheat production varies from 12 inches in the 
western part to 24 inches in the eastern part. The soil varies in 
texture from a light volcanic ash in the western part to a rather 
heavy basaltic clay in the higher eastern portion. Thus we have 
rainfall, soil density, altitude, and bunt intensity all increasing in 
the direction of the prevailing wind as we proceed northeastward 
from a point near The Dalles on the Columbia River. 
As a result of the climatic differences, harvesting operations begin 
in the western part about July 1 to 10'and move eastward, finishing 
in the extreme eastern portions some time in September. There 
are three methods of harvesting -i. e., binding, heading, and use of 
the combined harvester. 
The entire wheat region under consideration is summer fallowed. 
In the drier parts a crop, is raised m alternate years. Where the 
rainfall is heavier, summer fallowing is practiced once in three years, 
winter wheat following the fallow and spring grain the winter wheat. 
