Aug 4, 1923 
Systemic Infections of Rubus with Orange-Rusts 
235 
kled, and devoid of hairs. The petioles tended to elongate abnormally. 
Some of the axial buds were also beginning to proliferate. The distribu¬ 
tion of stomata on the leaves which appeared to be normal and on those . 
showing signs of infection was studied. Practically the same number 
of stomata was found on the underside of both kinds of leaves. There 
were only a very few on the dorsal side of the normal leaves, occurring 
mostly at the tips of the serrations. On the other hand stomata were 
thickly scattered over the upper epidermis of the abnormal leaves 
where they showed yellowing. Although no pycnia or aecia are present, 
the occurrence of large numbers of stomata on the upper side of a black¬ 
berry leaf is proof that the orange-rust hyphae have invaded the leaf. 
The first aecidia appeared April 3. If spermogonia were ever formed on 
these rusted plants they must have been “vestigial.” 
The writer had about the same number of systemically infected 
plants growing under similar conditions at the time, so it was possible to 
compare blackberries in which the infection had been of long standing, 
at least two years, with those showing the rust for the first time. The 
canes of the former were less angular and showed fewer thorns. Pycnia 
appeared all over the leaves as soon as they began to unfold. Every leaf 
at each node was dwarfed and yellowish from the start. Stomata were 
pretty evenly and thickly distributed over the upper surface between the 
pycnia. Here also it was found that there were about the same number of 
stomata on the underside of the normal and of the infected leaves per 
unit area. The total number of stomata per unit area was estimated to 
be fully 50 per cent greater on the infected leaves. Normal leaves from 
certain uninfected canes of this plant showed only a few stomata on the 
upper surface of the tips of the serrations. 
A further discussion of the effect of the orange-rusts on the develop¬ 
ment of stomata is being published in another paper. Unless one were 
very familiar with the appearance of various types of primary infections, 
he would have passed over the writer’s plants which had been infected 
the preceding summer because no spermogonia could be found. At the 
same time the plants that were secondarily infected showed the character¬ 
istic symptoms of having the orange-rust. 
SPECIALIZED RACES 
Since the long-cycled rust is fairly common on black raspberries in 
localities where the teleutospores have not been found on the black¬ 
berries, the possibility of the existence of strains or biologic races should 
not be overlooked. Whether the blackberry or dewberry can be infected 
with aecidiospores from the Gymnoconia on black raspberry or vice 
versa has not been definitely questioned by previous investigators. 
Morphologically the long-cycled rust on black raspberry has not been 
found different from the rust on blackberry. The writer has made a few 
preliminary experiments to see how readily the teleutospore stage could 
be obtained on one species of host by sowing aecidiospores from another 
variety. These tests are regarded as merely suggestive. 
On May 18, 1921, young leaves of new shoots of wild black raspberries 
at Bell, Md., were inoculated with aecidiospores from the mountain black¬ 
berry. On August 20, several teleuto sori were found on one of the lower 
leaves of one plant. The plants were well isolated in a hedge row 30 
rods from any orange-rust. If leaves on old canes had been present when 
the inoculation was made, no doubt the infections would have been more 
abundant. Two hybrid blackberry plants, wit* 1 predominant mountain 
