240 
Journal of Agricultural Research 
Vot. XXV, No. s 
So far as controlling the short-cycled rust in the cultivated blackberry 
is concerned, the writer’s experimental work is showing that it is per¬ 
fectly practicable with a small amount of labor to prevent the spread 
of the rust. Primary infections by spores occur comparatively rarely 
in nature; thus, if one observes proper care for a period of two or three 
weeks in early spring as soon as the first leaves appear, he can readily 
detect and destroy rusted canes before the mycelium has spread far into 
the underground perennial structures and before the spores are shed. 
The eradication of all rust from a field of blackberries where the dis¬ 
ease has been of long standing would be a more difficult undertaking. 
In New Jersey and in other states one can find fields where from 25 per 
cent to 75 per cent or more of the plants are infected. Such fields should 
be planted to some other crop unless the grower is willing to follow up 
and destroy all roots connected with the rusted plants. 
The work at Arlington, Va., reported above, affords a very good illus¬ 
tration of the efficacy of removing infected plants as soon as they show 
rust for the first time. The writer had about 130 cases of primary 
infection; wherever the rusted canes were pulled up so as to include all 
parts of the root runner which showed signs of infection, no rust appeared 
in 1923. In several cases where it was recorded that undoubtedly 
pieces of roots bearing mycelium were left in the soil, rusted plants 
showed in 1923. 
Probably one reason why infections by sporidia of the short-cycled rust 
are comparatively so rare when one considers the vast number of aecidio- 
spores that are matured, is that these spores are rather waxy and there¬ 
fore, like waxy pollen, are not blown for any great distance by the wind. 
It would not be good practice, in any event, to allow a rusted plant to 
remain in the field or to encourage a luxuriant growth of rusted wild 
blackberries in the vicinity of susceptible cultivated varieties. Two or 
three days of wet weather at the time new shoots are springing up would 
certainly result in a further spread of the disease by spores from plants 
near by. The rust can pass over just as easily from a wild blackberry as 
from a cultivated variety. 
SUMMARY 
(1) A study has been made of the distribution of the gametophytic 
mycelium of the short-cycled orange rust in the blackberry and dewberry, 
and of the mycelium of the long-cycled rust in the blackberry, dewberry, 
and black raspberry. In the canes of the blackberry in which either rust 
has become firmly established as a perennial parasite, hyphae are mostly 
confined to the central pith and to the fundamental tissue of the growing 
regions. At the nodes traces of mycelium are sometimes found along the 
rays in the wood and in the cambium and phloem. Hyphae penetrate 
the roots very extensively, following the cambium and sieve tubes of the 
root runner many feet. The cortex is also attcked. Very little mycelium 
is present in the woody tissue; there is no central pith in the root. New 
plants arising from the infected root runners will be infected. The 
spread of the rust from plant to plant in nature occurs frequently through 
the connecting roots. Mycelium invades the roots and rootlets of in¬ 
fected dewberries very generally but does not follow a root to any great 
distance. The rust is carried to new plants formed at the rooting nodes 
by the invasion of these sprouts by hyphae from the vines where the 
mycelium is distributed in about the same way that it is in the canes of 
blackberries. 
