497 
Sept .!„ 3 Effect of Orange-Rusts-on Stomata 
The gametophytic mycelium of Gymnoconia does not always penetrate 
into every part of the leaf of, for example, the black raspberry. One-half 
only may be infected; variegations occur or angular patterns are laid 
out, the space between certain large veins escaping attack. Photo¬ 
graphic prints can be made directly from these leaves, either before or 
after the chlorophyll has been extracted (PI. i). It will be found that 
production of stomata on the upper side of the leaf is coincident with the 
invasion of an area by the orange-rust hyphae. Plate i, C, shows that 
the infected area of the raspberry leaf is sharply limited on the left side 
by the vein, and toward the tip on the right side the mycelium has spread 
out part way between the second and third veins. There were no stomata 
on the dorsal side of this leaf, except over the infected areas. A some¬ 
what different pattern was worked out in the leaf shown as Plate i, A. 
Dorsal stomata occurred on the left side except at the base, into which 
Fig. i.—R elative numbers of stomata on corresponding areas from the ventral and dorsal sides of a leaf 
from an old cane of Rubus occidentalis infected with the long-cycled orange-rust. Position of stomata and 
spermogonia determined with the aid of a camera lucida: size and shape of stomata purely diagrammatic. 
In fact, the stomata on the dorsal side are on the average somewhat larger. Circles represent positions of 
spermogonia. The fields diagramed are such as were covered by a 16 mm. lens and Leitz Periplane icx 
P cu * ar ‘ ^A, Area from ventral surface; B, Similar area from the dorsal side nearly opposite the area shown 
m , t J here were I 5 ° stomata in the area from the ventral side, and 136 in the dorsal area opposite. It 
would be necessary to examine several such fields before a single stoma would be found on the dorsal side 
of an uninfected leaf, or of an uninfected part of this same leaf. 
hyphae had not penetrated. The lighter areas on the terminal and left 
lateral leaflets (PI. i, B), represent portions invaded and where dorsal 
stomata were numerous. The leaflets which escaped infection had no 
stomata on the upper side. Plate i, F and G, shows prints of leaflets of 
Kittatinnv blackberry on parts of which aecidia were just maturing. 
Practically the same number of stomata was found on the upper and 
lower sides on areas infected. 
The time intervening between the opening of a particular infected leaf 
on new canes and the maturing of aecidia on that leaf becomes progres¬ 
sively shorter as the season advances, until a time is reached when fully 
formed aecidia are exposed as the leaf opens. What should be the effect 
of such an early appearance of aecidia on the underside of the leaf ? The 
development of stomata on the underside is, just as we might expect, 
greatly interfered with, there being only a few normal stomata on that 
side, and these are at the tips of the serrations upon which no aecidia 
appear, just the reverse of the distribution of stomata in the normal leaf. 
An accurate count of the stomata has not been made on any considerable 
number of areas of normal and of infected leaves, but it is certainly inter- 
