140 
Journal of Agricultural Research 
Vol. XXIII, No. 3 
typical appressoria are formed. Plate 3, D, shows a tangential view 
of a stoma with the fully formed appressorium fitted closely to its outer 
surface. A withered remnant of germ tube is still attached at a, the 
four nuclei are located near the center, and by looking down through the 
cytoplasm of the appressorium one can see the narrow stomatal slit. 
These appressoria are formed in great numbers, and when the spores are 
abundant on the leaf, two, three, and even four appressoria can be seen 
crowded together at a single stoma. 
As was stated in a preliminary account of this work (1), relatively 
few of these appressoria pass through the stomatal slit in Kanred to 
form mycelium within the host. Six days after inoculation only 5 out 
of 100 appressoria had entered. Material taken 8, 10, and even 12 
days after inoculation still showed numerous appressoria and relatively 
few infections. Moreover the plants were not uniform as to the per¬ 
centage of entries. Of two plants grown side by side in the same pot 
and fixed at the same time, one might show very few entries and the 
other a percentage considerably above average. For greater accuracy, 
counts were made and the results presented in Table I. 
Table I. —Percentage of entries in Kanred at different dates after inoculation with rust 
Number of 
days after 
inoculation. 
Total number 
of fungi 
counted. 
Number of 
entries. 
Percentage 
of entries. 
6 
IOO 
5 
5 
8 
133 
14 
IO-f 
10 
77 
7 
9 
12 
i 45 
16 
11 + 
Under the conditions of this experiment only about 10 per cent of the 
fungi enter. The other 90 per cent remain outside the stomata until 
they dry and fall off. 
Plate 3, D, represents an appressorium fixed 6 days after inoculation. 
Eight days after inoculation the majority are still vigorous. A few, 
however, show signs of degeneration. Plate 3, E, represents a longi¬ 
tudinal section through a stoma on which at a is the shrunken appres¬ 
sorium with vacuolated cytoplasm and scarcely distinguishable nuclei. 
After 10 days the majority of the appressoria are withered, but a few 
(PI. 3, F) are still vigorous. By the twelfth day under greenhouse 
conditions practically all the appressoria are withered and collapsed 
(PI. 3, G). In the open, especially if subjected to a wind, the death of 
the appressoria probably would take place sooner. 
A brief comparative study of Baart shows that the fungus enters 
much more readily. Four days after inoculation 26 out of 39 appres¬ 
soria, or 67 per cent, had entered the host. 
The stomata of living leaves of Kanred were studied and drawn during 
early afternoon of a bright day when some of the stomata under green¬ 
house conditions are wide open. These drawings were measured as to 
length and breadth of the stoma as a whole, and the slit was measured 
in length and width. Plate 4, A, represents the average of these measure¬ 
ments. Using the same methods, and the same magnification, an aver¬ 
age stoma of Early Baart was drawn (PI. 4, B). 
