214 
Journal of Agricultural Research 
Vol. XXV, No. 5 
so several types of leaves with respect to age and position on the canes 
were exposed to infection. The leaves on the old canes were the most 
susceptible each year. 
Leaves of the black raspberry were infected with the telial stage by 
sowing aecidiospores from the blackberry, and the southern dewberry, 
Rubus enslenii , was likewise infected by sowing aecidiospores from the 
Black raspberry. Other species or varieties of Rubus said to be immune, 
or at least very resistant, to the orange-rust stage were infected with 
the telial stage. 
The conditions under which leaves of Rubus are most readily infected 
with the sporophytic or <l Puccinia peckiana H stage is outside the scope of 
this paper. This phase of the work is being considered in another paper on 
the effect of orange-rust on the development and distribution of stomata. 
SYSTEMIC INFECTION OF RUBUS OCCIDENTALS WITH SPORIDIA OF 
THE LONG-CYCLED RUST 
In infection experiments with the systemic stage of these rusts, the 
ordinary means of checking results by the use of isolated control plants 
alone does not provide sufficient safeguard. No one can explain or 
account for the results reported by Atkinson (2) on any other basis. 
A blackberry or raspberry may be infected in its underground parts 
without showing the rust on the aerial parts every year, so it would be 
unsatisfactory to use as experimental plants those which have just been 
received from a nursery or have been dug up in nature. An infected 
plant may be transplanted during the spring before the leaves are out 
and develop leaves normally in the greenhouse without showing rust 
that season, especially if it recovers only slowly from the shock of trans¬ 
planting. Since the presence or absence of mycelium in a cane or root 
can be demonstrated without question, one can be certain by using 
only tip shoots obtained from rooting canes that the raspberry which 
he inoculates is uninfected at the beginning of the experiment. It is 
not necessary to provide control plants in checking up the results. 
methods 
The methods used in preparing sections of canes or roots to demon¬ 
strate the presence of mycelium are the same as those adopted in the 
writer’s work on Gymnosporangium. Transverse sections 10 to 50thick 
stained with acid fuchsin and iodin green show hyphae and haustoria very 
plainly under the microscope. Longitudinal sections show hyphae much 
better, especially where they burrow along between the cambium and 
the phloem—for example, near, the nodes of blackberries which have been 
primarily infected. It is very easy to overlook the hyphae in the cambium 
region if one does not prepare longitudinal sections. 
The habit of the black raspberry mentioned above, whereby the canes 
take root at their tips, provides a very efficient natural method of propa¬ 
gation. Since it is possible to examine these stolons to learn whether or 
not the fungus has in some way established itself previously in the plant 
to be used, it has been found advisable for purposes of inoculation to 
use the tip plants. 
The tip ends of some of the raspberry canes were wired to the soil in 
ordinary flower pots as soon as they began to mature sufficiently to take 
root. After a few days, leaves of black raspberry bearing teleutospores 
were laid over the rooting tip ends and kept moist under muslin damp 
chambers for several days. 
