3«4 
Journal of Agricultural Research voi.xxvii.No. fr 
rust, and the relation of the physicochemical properties of the plant 
sap to rust resistance. 
ENTRANCE OF THE GERM TUBES OF PUCCINIA GRAMINIS 
The factors influencing the entrance of the germ tubes of Puccinia 
graminis into the host, which have been studied by the writer, are the 
number of leaf hairs, the number of stomata, the size and movement of 
stomata, and the relation of the formation of appressoria to subsequent 
infection. 
Relative Number of Leaf Hairs 
In order to compare the number of hairs on different varieties of 
wheat, the leaves of seedlings, 12 days old, were placed in aceto-alcohol 
(glacial acetic acid and 95 per cent alcohol, 1 part each) for several days. 
The pigments were so thoroughly removed by this process that the 
leaves could be mounted entire on a slide and observed with direct 
light under the binocular microscope. The hairs on leaves thus treated 
can be seen distinctly and can be counted easily. 
As shown in Table I, there is a consistent difference in the number of 
hairs on the leaves of the five varieties of wheat used in this study. Kota 
always has the most and Tittle Club the fewest. Observations on leaves 
from the field at heading time show the same general differences. No 
hairs were found on the culms of any of the varieties observed. 
Table I.— Comparative number of hairs on the two surfaces of leaves of five wheat varieties 
[Average of io microscopic fields ( 2.138 sq. mm.).] 
Variety. 
Kota, C. I. 5878: 
Lower surface. 
Upper surface. 
Khapli, C. I. 4013: 
Lower surface. 
Upper surface. 
Kanred, C. I. 5146: 
Lower surface. 
Upper surface. 
Marquis, C. I. 3641: 
Lower surface. 
Upper surface. 
Little Club, C. I. 4066: 
Lower surface. 
Upper surface___ 
' On midrib. 
Edge of blade. 
Average 
for leaf. 
Average 
both 
surfaces. 
Distance from tip. 
Distance from tip. 
1 inch. 
2 inches. 
1 inch. 
2 inches. 
106 
105 
98 
IOI 
3 S' 
H M 
99 
94 
H M 
O O 
K> GJ 
} 5 
61 
56 
85 
80 
70 
> C7 C 
54 
27 
53 
46 
45 
j 5/* j 
20 
29 
24 
32 
26 
l 78 a 
35 
27 
3i 
28 
% 3° 
/ stO* \J 
5 
4 
8 
5 
6 
} 13* 5 
23 
16 
24 
22 
21 
1 
6 
1 
8 
4 
\ 
12 
14 
11 
20 
14 
/ 9-o 
The five wheat varieties listed in Table I were inoculated on the first 
leaf with urediniospores of Puccinia graminis tritici i Form XXXIII, and 
allowed to incubate 48 hours, when they were placed on the greenhouse 
bench. Two days later some of the inoculated leaves were removed and 
cleared in aceto-alcohol for several days. The entire leaf was then im¬ 
mersed in Pianeze stain for one minute and then washed thoroughly in dis- 
