Aug. 4, 1923 
Systemic Injections of Rubus with Orange-Rusts 
221 
19 21 
develops a horizontal root 1 or 2 feet long, from which arises, in 1921, 
a shoot in condition for infection. If inoculation is successful, it will 
be manifested about April, 1922, by the appearance of rusted shoots 
from the base of the 1921 plant. If examination of sections of the 
horizontal root connecting the parent plant with the one inoculated fails 
to show hyphae, it is certain the rust did not come from the parent. 
The mere fact that a plant shows no rust on its leaves is not proof that 
the mycelium is not well established in its crown or in the root runners; 
but if the runner bearing an infected cane shows no mycelium, the infec¬ 
tion must be a new and independent one, regardless of the fact that the 
parent plant may ajso be rusted. In this way it will be shown that a root 
runner may bear two or three infected 
plants along its course and each plant be 
separately and independently infected. 
Inasmuch as potted plants can not send 
up shoots from roots at an appreciable 
distance from the parent plant, they are 
not as satisfactory for. infection experi¬ 
ments as are those grown in “flats” on the 
bench or as are field plants where shoots 
are formed on roots 2 or 3 feet from the 
parent. The Iceberg variety appears es¬ 
pecially favorable for the production of 
root shoots. By digging in the soil, still 
younger shoots can be exposed when they 
are in a very susceptible condition. 
As an illustration of this phase of the 
work attention is directed to figures 4 and 
5 which are diagrams of a part of the root 
system of plant No. 134, May 6, 1922. 
The inoculation frame would have covered 
the six plants, figure 4 (+ ), which became 
infected and probably took in either M or 
N ( —) which were not infected. Plant 
P' was not inoculated although it was a 
young shoot 5 or 6 inches high when the 
others were inoculated May 23, 1921. 
Figure 5 shows how clear-cut the original parent nursery stock remained. 
There are no shoot buds present on it such as are always found on this 
vertical underground structure when it harbors mycelium of the orange- 
rust. The roots N and C arise close together, yet C now bears an in¬ 
fected plant while the one from root N is rust free. The convincing 
evidence that the parent plant, P, P', is not already parasitized is 
obtained only by making sections of the root bearing the new plant. 
Pig. 4.—Diagram showing arrangement of 
inoculated plants and roots connecting 
them with parent Crystal White black¬ 
berry, No. 134* Nursery stock, P, P', 
planted in 1920. Other plants indicated, 
larger circles, were young shoots in May, 
1921, when the experiment was made; 
small circles attached, new shoots, 1922. 
Infection frame probably covered area 
about NEA. Numerals represent dis¬ 
tances in inches. Signplus + indicates 
plant infected May, 1922, when dug; 
roots bearing plants A and B broken off 
in digging; sign — indicates uninfected 
plant. See text and figure 5 for further 
explanation. 
resuets 
When one studies blackberries in nature, he becomes familiar with those 
which are infected, and can recognize them after the leaves have fallen. 
Even though the canes may not be particularly stunted, their appear¬ 
ance and the size of the buds are such as frequently to enable one to pick 
out the diseased plants. The writer’s experimental plants were there¬ 
fore examined with considerable interest at intervals from June until 
November following the inoculation experiments. Only one plant was 
found, September 28, which suggested that the inoculation had been 
