Auf. 4, 19*3 
Systemic Infections of Rubus with Orange-Rusts 
225 
PRIMARY INFECTION BY THE SPORIDIA NOT BECOMING SYSTEMIC 
Local infection with the sporophytic stage by aecidiospores is, of 
course, the rule with the Gymnoconia. The question has frequently arisen 
whether local, as contrasted with systemic gametophytic infection by 
sporidia, may not sometimes also occur. One frequently sees rusted 
leaves on certain branches or nodes, while the leaves at all the other nodes 
of the same cane remain free. The writer made sections of several such 
naturally infected canes at points above and below the nodes bearing 
rusted leaves. Having found hyphae in the pith in each case, he came 
at first to the erroneous conclusion that infection by Kunkelia is always 
systemic, the rust appearing more tardily on some leaves, or not at all if the 
mycelium happened not to penetrate the leaf primordium at an early stage. 
Later an exception was noted which remained a puzzle until the results of 
inoculation experiments became available. A sand blackberry at 
Cameron, N. C., was found May 2, 1921, with rusted leaves at only one 
or two nodes of its single “ old ” cane, which was otherwise perfectly 
normal. Sections of the cane at the base and at points above the 
affected nodes showed no hyphae in the pith, indicating that in nature 
“local” infections are possible. The proof of such infections has become 
conclusive as artificially infected plants have been studied. One clear 
case noticed was that on plant No. 24, a wild blackberry showing no 
signs of infection February 14, 1921, when it was transplanted. After 
it was potted it grew vigorously, showing no rust during the year. On 
March 22, 1921, it was sprayed with sporidia and kept under a damp 
chamber three days. The plant was taken from the cold frame January 
12, 1922. Leaves soon appeared on the old canes and new shoots 
grew up, but the plant was perfectly normal, no rust having developed. 
It has been found that when infected plants are kept from year to 
year, the leaves of new shoots that push out a few days after the plants 
are brought into the greenhouse are usually covered with pycnia before 
they unfold. It was, therefore, surprising to find two months later 
(March 19) that rust was beginning to show on this plant. The tip 
of the old cane had died during the winter, but from the uppermost 
living node a new shoot had recently developed. The leaves of this 
new branch now bore aecidia. Sections at the base of this cane showed 
no mycelium in the pith, phloem, or cortex. Just below the infected 
node, however, hyphae were found in the cambium region and along 
the medullary rays, but none in the pith. A critical study of the dis¬ 
tribution of the mycelium in the cane showed that the parasite had 
originally gained entrance through an axial bud which must have been 
at least 3 inches above the ground. The end of the cane had died 
during the winter, but hyphae were making their way slowly down 
the cane in the region of the cambium, which it was stimulating to 
renewed growth. This was indicated by a second annual ring of wood 
which was being formed (PI. 2, D, y), the cane at this point being larger 
than at the base. The plant was then set out in soil on the bench in the 
greenhouse,where it has since grown vigorously without showing any signs 
of being infected. It is clear that the cutting out of the one cane which 
showed rusted leaves at a single node freed the plant entirely from the 
parasite. Had the infected cane been allowed to remain, it is doubtful 
whether the hyphae could have reached the perennial parts below the 
ground before the cane would have naturally died. Several other cases, 
54483—23 - 2 
