Aug. 4,19*3 
Systemic Infections of Rubus with Orange-Rusts 
233 
to explain on any other basis because of the absence of an old cane at 
the point where infected shoots were then growing. More careful 
search at such times usually showed the stub-end or scar of a cane which 
had been cut or borken off accidently or which had died the previous 
summer. In the absence of such structures through which the parasite 
might have entered the root, one naturally suspects that the mycelium 
has traveled along the root runner from some other infected plant. If 
such a possibility is precluded by an examination of sections, one would 
have to consider the alternative—direct root infection, which could 
occur only on exposed roots and before the cork covering had been laid 
down, or through wounds. For example, in one case it was found that 
the manner of infection could not be determined at first because of the 
absence of any remains of, or evidence of, the existence of the orginally 
infected shoot. Several shoots of the Mercereau (No. 352) blackberry 
were sprayed with sporidia April 25, 1921. No inoculating chamber 
was used. On May 8, 1920, aecidia were found on three plants, No. 
352 A and B showing the ordinary type of primary infection. Old 
canes which were rather small and somewhat dwarfed were present 
and infected shoots were growing from the base of each. There was no 
old cane nor any trace of a stub or scar showing where one might have 
been, in connection with plant No. 352 C, the third plant infected. Two 
new shoots, both infected, and about a dozen buds were growing 
from a horizontal root where it was somewhat enlarged (PI. 7, A). 
Thirty-two inches from these shoots the basal end of an old cane b, 
was found. The small root runner was followed 14 inches farther where 
it was attached to a larger root having several branches, c. This root 
had its origin 18 inches away in a large perfectly normal cane now in 
blossom. Sections of the horizontal root were made at points as follows: 
One foot from the parent plant; c 2 , 6 inches beyond the stub of the 1921 
cane; c 5 , 3 inches from the first rusted shoot which was sectioned at 
c 4 . No mycelium was found in the root sections, proving conclusively 
that the infection had not been carried over from the parent plant. 
Hyphae were found in the pith only of the infected shoot, c 4 , as was 
expected. It was observed that the second shoot was somewhat woolly 
at its base and had a number of scale leaves about one inch from the 
point of attachment, indicating that this part of the shoot had been 
formed the previous summer. This could not have been the shoot 
originally inoculated and the one which had remained dormant after 
infection. 
It has been noticed that where shoots of the witch’s broom type grow 
up early in the spring they are often woody at the base, which is cov¬ 
ered with scale leaves. The buds are forced out the preceding autumn, 
lie dormant over winter, being protected by a covering of soil, and push 
up early in the spring. Such conditions are easily found in naturally 
infected plants. In the case being considered, it is possible that the root 
had been exposed about the time the inoculation of other shoots had been 
made and the fungus entered the root probably through a wound. 
Since shoots devoid of chlorophyll can be most easily infected and since 
the fungus can thrive in underground parts, there is no evident reason 
why very young roots may not be directly infected through unprotected 
epidermis or through wounds extending to the cambium. Evidence 
in support of such a probability was found in connection with No. 35 7E, 
a photograph of which is shown in Plate 7, B. The parent stock, planted 
in 1920, still bore large healthy canes in 1922. One other old cane 
