Nov., 192 1 ] HOERNER 
In the field, the soil beneath cereals heavily rusted with P. graminis Pers. 
is often found literally covered with fallen urediniospores. The idea has 
been conceived that seedlings penetrating such soil might become infected 
and the rust be aided in its spread in this way. Greenhouse experiments 
have proven this possible, it is reported, with P. graminis Pers. In order 
to determine if such infection is possible in the case of P. coronata Cda., 
the following experiment was devised: 
After soaking in water for twenty-four hours, six oat seeds were planted 
about one half inch deep in each of four four-inch pots of a uniform soil mix- 
ture. The surface soil was then heavily dusted with fresh viable uredinio- 
spores. These pots were then placed in a ventilated cage to avoid possible 
chance infection of the seedlings by air-borne spores. Watering was avoided 
in order to prevent germination of the spores before the seedlings should come 
in contact with them. After ten days' time none of the twenty-two seedlings 
that developed showed any signs of infection, though guttation occurred 
from the seedling leaves, affording optimum conditions for spore germi- 
nation. 
These results indicate at least that seedling infection caused by emer- 
gence through soil densely covered with viable urediniospores does not 
occur readily. This condition may possibly be due to the fact that the 
sheath which surrounds the emerging seedling is not supplied with stomata 
and therefore affords no opportunity for the entrance of the germ tubes. 
Ill 
The possibility of urediniospore-producing mycelium overwintering in 
the host plant and producing a new crop of urediniospores in the spring, 
together with the overwintering of urediniospores in the field, was considered. 
Christman (3) found, under Wisconsin conditions, viable urediniospores 
at any time during the winter with a three-months' period during which 
the temperature hovered about the freezing point. Urediniospores from 
oats, developed upon protected plants during the winter, germinated as late 
as January 26. Indications were that the mycelium would be as resistant 
as the host within which it grew. Old spores remained viable for some 
time, though new crops of spores from overwintered mycelium seemed to 
be the more important mode of spring infection. 
Reed and Holmes (4) found viable urediniospores on oats throughout 
the year under Virginia conditions. They conclude that the crown rust 
on oats has an enduring mycelium capable of producing a new crop of spores 
during much of the winter, and although spore production ceases during 
midwinter, the mycelium, upon the advent of warm weather, is capable of 
producing new crops of viable spores. 
The urediniospore-germination studies that the writer has performed 
would seem to indicate that under Minnesota conditions urediniospores 
