Feb. 9,1924 
Resistance of Wheat to Puccinia graminis tritici 
385 
tilled water. The leaf was then mounted entire on the slide and examined 
with direct light under the microscope. It was observed that the germ 
tubes often came in contact with hairs and entwined about them. It is 
believable that this might reduce the number of germ tubes which are 
able to reach the stomata and form appressoria. Table V shows that on 
Kota, the variety with the largest number of leaf hairs, the actual number 
of appressoria observed on the average leaf is lower than that on varieties 
with fewer hairs, although enough appressoria were developed to permit 
infection. In these experiments, therefore, the leaf hairs could not be 
considered as a serious obstacle to entrance. If the inoculum is abundant, 
and other factors are favorable, the number of hairs on wheat leaves prob¬ 
ably has very little effect on the final degree of infection. On the other 
hand, if the opportunities for germination and germ-tube development 
are not particularly favorable, it is possible that a large number of hairs 
may reduce the number of infections somewhat. 
Relative Number of Stomata 
As the germ tubes of Puccinia graminis must enter the wheat plant 
through the stomata, it seems possible that entrance would be easiest in 
those varieties in which there are many stomata per unit area of surface. 
Thus it would be important to know lie comparative number of stomata 
on varieties which show marked differences in resistance. The varieties 
under investigation were grown in adjacent rows in the plant pathology 
field plots at University Farm, St. Paul, Minn. 
The relative number of stomata on the neck of the stem was first deter¬ 
mined. Three varieties were selected: One resistant in the field, Kota, 
C. I. 5878; one susceptible, Little Club, C. I. 4066; the third moderately 
susceptible, Marquis, C. I. 3641. These host reactions are based on gen¬ 
eral behavior to stem rust at University Farm under conditions of an 
induced epiphytotic. At the time the grain was in the hard-dough stage 
the peduncles, from the upper node to the rachis, were cut and killed in 
aceto-alcohol. 
Table II shows the actual counts made on strips of epidermis from 
several stems of each variety, and represents the average number in 10 
microscopic fields. The number of stomata on Little Club, the suscep¬ 
tible variety, was considerably higher per unit area than that on the other 
varieties. 
Table II .—Number of stomata per microscopic field (. 1.150 sq. mm.) on peduncles of 
three wheat varieties 
Variety. 
Distance from rachis. 
Average. 
0.5 inches. 
2.5 inches. 
Little Club, C. I. 4066. 
156 
112 
134 
Marquis, C. I. 3641. 
112 
69 
90 
Kota, C. I. 5878. 
95 
41 
68 
In Little Club, also, the bundles of sclerenchyma fibers are far apart; 
in Kota they are closer together and often allow for only a single row of 
stomata. (PI. 1, C.) 
