Aug. 4,1923 Systemic Infections of Rubus with Orange-Rusts 211 
blackberries growing together in nature, he often finds several infected 
plants attached to the same root. The writer has made sections of such 
connecting root runners and has found an abundance of mycelium in 
the medullary rays, in the phloem near the cambium, and in the cortex 
for many feet, or as far as the runner extends. Ordinarily but little 
mycelium will be found in the woody portion of the roots except along 
the medullary rays. More rarely hyphae are scattered irregularly in the 
wood; this usually occurs in the case of recent primary infection of root 
shoots by spores where there has been an increase in the amount of 
porous wood tissue formed as the result of the late invasion of the root 
by the parasite. 
The distribution of the mycelium was traced in the canes and in the 
root system of a certain colony of infected wild blackberries at the time 
of year when rust pustules were maturing. There were found at a point 
(A in fig. 2) the remains of dead canes in the form of a witch’s broom 
characteristic of plants infected by this rust. Large roots extended 
downward into the soil. From one root which was of the runner type 
Fig. 2 .—Diagram of a series of wild blackberry plants April, 1921, arising from the same root runner (part 
shown here about 6 feet long). A, dead canes of 1919 plant in form of a witch’s broom; B, old cane (heavy 
line) and new shoots showing rust; C, stub of dead cane, new shoot rusted; D, old cane in blossom, not 
rusted; E, witch’s broom consisting entirely of new shoots; sections of the regions 1, 2,3,4, and 5 0# the 
root showed hyphae in the phloem and cortex. The plant D escaped infection through some accidental 
failure of the root mycelium to penetrate the shoot bud in time. 
new shoots and old canes (B), now rusted, were arising at a distance of 
18 inches. At C, io inches beyond, another plant, composed of rusted 
shoots, was attached to the same root; the old cane had died. Two feet 
farther (D) the plant from the runner consisted of one old cane in blos¬ 
som and free from rust. At E, 14 inches distant, was a witch’s broom 
of infected new shoots. Sections were made of the root runner at points 
on both sides of each plant; mycelium was found in the phloem and 
cortex in every case, demonstrating clearly the method by which the 
rust spread through the root system. Hyphae have been found in the 
ordinary type of root 18 inches below the ground. A plant arising from 
a runner bearing mycelium may rarely be devoid of rust (plant D noted 
above) due to the failure of the mycelium to enter the shoot at the time 
of its origin, just as rust-free canes are found in an infected hill. If 
the rust enters a shoot bud from underground parts, hyphae will later 
be found only in the pith of the cane, except at the nodes. In these 
regions hyphae may grow along the rays or outside of the wood ring. 
The blackberries studied in the vicinity of Washington, D. C., and at 
Cameron, N. C., were infected with the short-cycled rust. Specimens of 
