Aug. 4, 1923 
Systemic Infections of Rubus with Orange-Rusts 
215 
INFECTIONS IN THE GREENHOUSE 
About the middle of January the inoculated plants were trans¬ 
ferred from the cold frames to the greenhouse. As soon as new 
shoots appeared it was evident that a number of the experiments had 
been successful. Fifteen plants which had been propagated by rooting 
the tips of rust-free plants were inoculated during August and Sep¬ 
tember, 1921. Nine of these plants developed aecidia the following 
spring. An examination was made of the cane from which each 
new plant had been derived, material for sections having been 
obtained at the time the new plant was separated from its parent. 
No hyphae were discovered in any of these canes. As a double check 
when the rust began to show, another set of sections was made of 
that part of the original stolon still attached to the new plant. Sections 
were also made of the tip ends of such canes as had grown forward after 
they had taken root, so it is evident that the nine plants now showing 
rust were uninfected at the beginning of the experiment. The parasite 
must have gained entrance in each case as the result of inoculation with 
Fig. 3. —Diagram of rooting tip of black raspberry, Rubiis occidentalis , No. 215, which was infected by 
laying leaves bearing telia over the tip. Shoots G and F bore pycnia at this time. Shoot buds C, D, 
E, and I were infected, but still beneath the soil; L, dormant bud. Sections at A and B showed no traces 
of mycelium. Sections of the stolon at L, O, K, and K' showed hyphae along the cambium and phloem, 
none in the pith. The young shoot buds, C and I, had hyphae in pith as well as in the growing region 
and among the bundles where differentiation was incomplete. 
sporidia from teleutospores and not from hyphae carried over from an 
infected parent plant. It was pointed out previously ,(p. 213) that in 
the internodes of an infected cane the mycelium is confined to the central 
pith. At or near a node, hyphae are sometimes found growing along 
the medullary rays in the wood and in the cambium and phloem regions. 
In any case, there will always be some mycelium in the central pith. 
It is due to this characteristic distribution of the hyphae that it is pos¬ 
sible to distinguish between cases of primary infections by sporidia and 
secondary infections where the mycelium enters a new cane directly 
from the infected parent plant. 
On February 18 one of the artificially infected plants, No. 215, was 
freed from soil and photographed (PI. I), and a diagram (fig. 3) was 
made in order to locate the regions or structures from which material 
was obtained for sections. The new shoot buds, figure 3, C, D, and E, 
3 mm. to cm. long, were pushing out, but had not reached the sur¬ 
face of the soil and were still without chlorophyll. At L there was a 
dormant axial bud near the base of which a few roots were attached. 
Sections of the stolon at B and of the roots and dormant bud at L showed 
