388 
Journal of Agricultural Research voi. xxvn. No. 6 
presented in Table IV failed to open. These days were very dark, there 
being no sunlight whatever. It seems that stomata! movement not only 
varies with different varieties of wheat, but varieties themselves evidently 
do not respond to a variable in exactly the same way. 
Experiments therefore were made to ascertain whether the stomatal 
behavior in any particular variety of wheat is an important factor in 
determining the number of stem-rust infections which result from a given 
number of spores germinating on the leaf surface. 
Relation of Formation of Appressoria to Subsequent Infection 
Seedlings of five wheat varieties which behave quite differently toward 
several biologic forms of P. graminis were heavily inoculated with viable 
urediniospores and placed in humidity chambers for 48 hours. The 
plants then were placed on the greenhouse bench for 48 hours. A number 
of leaves then were taken at random from each variety and cleared several 
days in aceto-alcohol. The remaining leaves were left in order to ascer¬ 
tain the number of uredinia which would develop. The cleared leaves 
then were submerged one minute in Pianeze stain, and washed in water to 
remove the excess stain. The leaf tissue which had been cleared by the 
aceto-alcohol did not take the stain, but the germinating spores, germ 
tubes, and appressoria on the leaf surface were stained purple red. The 
entire leaf was then mounted, and the germ tubes on its surface were 
observed in direct light. The results are given in Table V. 
Table V.— Relation between number of appressoria of Puccinia graminis produced on 
the wheat leaf and subsequent infection 
Wheat variety. 
Percentage of urediniospores 
germinating on leaf. 
Average 
number 
of appres¬ 
soria per 
leaf. 
Number 
inoculated 
plants 
infected. 0 
Average 
number of 
uredinia 
per leaf. 
INOCULATIONS WITH BIOLOGIC FORM XVIII 
Kanred, C. I. 5146. 
I 
17 
20 
7 
nr 
3. 2 
Tittle Club, C. 1.4066. 
1 Abundant; approxi- 
| mately 50 per cent. 
*n* 
2.8 
Kota, C. I. 5878. 
< *5 
19 
20 
2. I 
Marquis, C. I. 3641. 
V 
i 
2. 7 
Khapli, C. I. 4013.. 
J 
9 
Tr 
4.6 
y 
INOCULATIONS with biologic FORM XXVII 
Kanred, C. I. 5146. 
f 32 
44 
< 17 
$ 
O 
Little Club, C. I. 4066. 
Abundant; approxi- 
* mately 50 per cent. 
I 
2. 9 
Kota, C. I. 5878. 
* 
O 
Marquis, C. I. 3641. 
1 27 
l 23 
2.3 
Khapli, C. I. 4.013. 
* 
4.2 
a The denominator indicates the number of leaves artificially inoculated, and the numerator shows the 
number which became infected. 
