Aug. 4, 1923 
Systemic Infections of Rubus with Orange-Rusts 
213 
are not apt to become stolons and take root. In such plants the disease 
“runs out” because its host dies. Occasionally, some of the infected 
canes recover vigor and become stolons, in which case the mycelium 
passes from the stolon into the buds which arise to make new shoots at 
the point of rooting, thus spreading the disease to new plants. Sec¬ 
tions of the internodes of infected canes and of such stolons have always 
shown mycelium in the'pith, none in the phloem or cambium. Further 
consideration will be given this point in another connection. The dis¬ 
tribution of the hyphae in the underground parts of the infected black 
raspberry is practically the same as that found in the blackberry and 
dewberry, except that hyphae are very much more abundant in the 
woody tissues of both roots and stems of the raspberry. One black 
raspberry examined had been under observation for three years. Sec¬ 
tions of the large vertical underground stem bases from which the spind¬ 
ling canes were now arising, showed mycelium in the pith, scattered 
irregularly through the wood and along the medullary rays in the xylem 
- and phloem regions. No hyphae were found in the well-marked pith 
of the much enlarged and distorted rhizomelike structure from which 
roots were growing. 
The largest roots were only about 1 foot in length. The fungus was 
found throughout the wood, and especially along the rays for a distance 
of 8 inches in one root; and the presence of hyphae was demonstrated 
in seven other roots, each cut at about 3 inches from its point of origin. 
The fact that the dewberry and black raspberry are not propagated by 
root sprouts precludes the possibility of the spread of the disease through 
the roots. It is clear that the invasion of the roots by the mycelium is 
a matter of nutrition and is not correlated with the spread of the 
disease, as one might be led to believe if only the blackberry were 
studied. 
Although the orange-rust has been reported on the red raspberry, 
Rubus strigosus, the writer has been unable to obtain specimens for an 
investigation of the distribution of the mycelium of the systemic stage 
in this host. 
LOCAL INFECTION OF RUBUS WITH AECIDIOSPOREvS OF THE LONG- 
CYCLED RUST, GYMNOCONIA INTERSTITIALIS 
In order to obtain a supply of teleutospores for experimental pur¬ 
poses, it was found desirable, for example, to infect the black raspberry 
by sowing aecidiospores of the Gymnoconia from this host. It is well 
known that young apple leaves are much more liable to infection by the 
cedar-rust than are the older or more mature leaves. It was with this 
in mind, as well as to obtain shorter plants for inoculation, that the 
writer at first purposely pruned away the old canes in the potted plants 
used in the greenhouse work. Plants in nature having young shoots on 
which leaves were just unfolding were chosen in preference to those with 
the old canes present or with leaves that were more fully grown. Judg¬ 
ing from the results which followed, both practices were unwise, since 
it was found that the leaves on the old canes and the lower leaves on 
the new canes frequently bore telia, while the leaves which were just 
unfolding at the time the spores were sowed rarely became infected. 
The experiments were repeated the two following years, and in each 
test the tip ends of the raspberry canes were tagged at the points where 
the leaves were just beginning to unfold. Below the tags the leaves 
were fully expanded. Furthermore, the old canes were not cut away, 
