Aug. 4,1923 Systemic Infections of Rubus with Orange-Rusts 231 
growth is indefinite, the tip ends of the cane being regularly killed at 
the end of the season. This proliferating tip end was about a foot long. 
Sections of this 1921 cane 18 inches back of the tip at c showed mycelium 
only in the pith. The effect of the proliferating shoots along the cane 
may be seen by the partial second annular ring of wood being formed 
(PI. 2, C, y). At the swollen base (PI. 6, a') of the 1922 portion, mycelium 
was also found in the phloem and cortex leading to leaves from this 
swollen region. Sections of the new growth 2 inches above (a') showed 
mycelium only in the pith. Until extended study has been made of 
the actual point of penetration of the host by the fungus it will be 
impossible to say definitely when the parasite could have been estab¬ 
lished in the growing point of this old branch. Mycelium showed 
only in the pith, except at the nodes where it could be found in the 
phloem or in the cortex even. 
That the original point of infection is not ordinarily the terminal grow¬ 
ing region of the shoot is clear from the large percentage of artificially 
infected canes which show no mycelium in the pith at any point, and 
none at all in the cane along the greater portion of the upper region. 
It is possible that where the cane is broken off soon after infection, the 
axial buds in which the fungus has become established may be stimulated 
to grow out vigorously, and if the fungus were in the fundamental tissue 
of the growing region, it would later appear in the pith after tissue 
differentiation. The writer has observed no case where the main shoot 
inoculated behaved as though the terminal bud had been attacked, 
though this no doubt occurs occasionally despite the protection of the 
growing region, by overlapping leaf primordia. The rapidity with which 
young canes grow up undoubtedly enables them to outstrip the fungus, 
which at first seems to grow only slowly, so the mycelium would be left 
behind in the cortical and phloem regions. Hyphae then make their way 
slowly up the stem for a short distance and more rapidly downward into 
the underground stem, and even into the roots. Here the presence of 
the parasite stimulates the formation of buds, the growing regions of 
which will be invaded by the hyphae, and as these buds develop into the 
new shoots the following spring, the fungus, now firmly established, grows 
upward rapidly and will be found in the pith even at the tip of the new 
cane. 
The writer's experiments show that infection can take place when 
shoots are several inches high, but in such cases the fungus rarely grows 
downward with sufficient rapidity in northern latitudes to become 
firmly established in the perennial underground organs. The younger 
the shoot inoculated or the nearer the root the infection occurs, the 
more certain is the fungus to become systemic the following year. 
If plants are grown in flats in the greenhouse where the canes are 
prevented from becoming dormant until late, infection of large shoots 
at two or three nodes spreads rapidly through the cambium and phloem 
upward nearly the full length of the stem, and downward well into the 
root system. Such infections are thoroughly systemic, but no mycelium 
will be found in the central pith, and there will be no proliferating terminal 
bud. In the southernmost states where the growing season for black¬ 
berries is almost continuous one would expect this type of primary 
infection to be common in nature. 
