12 BULLETIN 1230, U. S. DEPARTMENT OF AGFICULTURE. 
MORPHOLOGIC RESPONSE TO PATHOLOGIC CONDITIONS. 
No general discussion of the morphology or cytology of the two 
Tilletia species peculiar to wheat will be undertaken in this bulletin. 
However, some recent observations deserve mention. Harwood (11) 
and Potter and Coons (IS) called attention to the difference in 
appearance between Tilletia laevis and T. tritici. They found that 
the latter has the property of shortening the culm to a much greater 
extent than the former. 
Edler {6) and Appel (1, 2) discuss the extreme differences in form 
between sound and bunted heads in wheat of the compactum type. 
It is a matter of common knowledge that the bunted compact um 
heads are generally much elongated and more slender; in fact, they 
approach the vulgar e type. To this rule, however, there are frequent 
exceptions. The large use made of club wheats in the Pullman 
experiments, on account of their susceptibility and the fact that in 
spite of this drawback they are desirable wheats for that section, gave 
exceptional opportunities for observing their characters in relation 
to bunt. These are treated to some extent by Heald and Wool- 
man (IS) i The exceptions occur more frequently in spring-sown club 
wheats than when sown in the fall. Ordinarily the bunted compact um 
head is abnormally elongated some time before it emerges from the 
boot. An examination at this time shows the stamens yellow and 
aborted and the ovary green instead of white and of abnormal size. 
A microscopic examination of their contents shows them to be full 
of nearly mature spores. In exceptional cases the head on emerging 
from the boot has an entirely normal appearance in both shape and 
color, and in due time the stamens are thrust forth normall}\ In 
these heads the shape remains normal until near ripening time when 
they reveal their character only by the spreading of the glumes. 
The culms supporting this type of head are of normal height or 
nearly so. Usually there are a few kernels of wheat in the head, and 
it is in this type that the partially bunted kernels are most likely to 
occur. The shortening of the culm is much more pronounced in the 
compactum than in the vulgar e type. 
To determine the age and stage of development at which a seedling 
becomes noninfectible and the extent of infectible area of the plumule, 
two experiments were conducted. Infested soil which was used in 
these experiments was prepared in the following manner: A mass 
of soil was autoclaved, dried, pulverized, and passed through a 10- 
mesh screen, after which it was mixed with 2 per cent of its weight 
of bunt spores. Eight or ten days before using, a portion was 
moistened to the proper degree and at intervals of two or three days 
other portions were so moistened. All were kept at a suitable 
temperature for spore germination. When used the portions were 
all mixed together and new dry spores added. Thus spore material 
in an infective stage was insured at the time it was used and lor at 
least two weeks subsequently. 
In the first experiment wheat was sown in sterilized soil, ami at 
definite stages of growth the plants were transferred to infested soil. 
The method of sowing employed in the first experiment was as 
follows: A pot was filled to the proper height and the soil shaken 
down and smoothly compacted. Sterilized seed of Hybrid L43 was 
placed on this surface and covered to tin 4 required depths with loose 
