Aug. 4, 1923 
Systemic Infections of Rubus with Orange-Rusts 
219 
orange-rust on black raspberry ordinarily spreads from plant to plant 
by means of sporidia which infect the rooting tips of canes in August 
and September. 
SYvSTEMIC INFECTION OF THE BLACKBERRY WITH SPORIDIA OF 
THE SHORT-CYCLED FORM 
There are clearly two strains of orange-rust on blackberries, the short- 
cycled form, “ Kunkelia,” and the long-cycled form, Gymnoconia, which 
has Puccinia peckiana as its teleutosporic stage. The writer is describing 
elsewhere blackberries that are infected with orange-rust of such a nature 
that spores in one aecidium all develop promycelia, and those in some 
adjacent aecidium all produce germ tubes. One should perhaps hesitate 
before adopting separate generic names even for the strains that appear 
to be well fixed. It certainly is to be regretted that the aecidiospores 
of the “Kunkelia” are sometimes referred to now as “teliospores.” 
This practice not only leads to confusion but has no basis in morphology. 
The pycnia of the short-cycled rust are said by Arthur (1) to be sub¬ 
cuticular. They are, of course, sub-epidermal, the same as are the pycnia 
of the Gymnoconia. Newcombe (8) and Clinton (j) illustrate sub- 
epidermal spermogonia of the orange-rust. 
methods 
During April and the first weeks in May, blackberries at the Arlington 
Farm, Va., send up shoots in large numbers from roots. By digging 
about shoots that have appeared above the ground, one can find white 
or reddish shoots in still earlier stages of growth. Some of these young 
shoots may be broken off or injured as one endeavors to uncover the 
youngest, but he can readily find places where a half dozen or more 
ranging from mere buds to shoots 6 or 8 inches high, are growing in a 
space covered by the infection frame. A large pan is set on sticks or on 
a frame at the desired place, and muslin strips are hung over the frame 
dipping into the pan, which is filled with water. This is the iceless 
refrigerator designed by Hunt (6 ). If the apparatus is shaded from the 
sun and the pan kept filled with water, a very efficient damp chamber 
will be provided for field work. Several methods of “inoculation” were 
tried, aecidiospores in each case being obtained from wild blackberries 
growing at Radnor Heights, near Rosslyn, Va. 
AECIDIOSPORES SOWED ON SHOOTS 
Leaves bearing aecidia were laid over young shoots, so that spores were 
shed naturally over growing tips, etc., or the spores were dusted over 
the shoots and into the leaf axils. In this way an excess of moisture 
which prevents proper germination is avoided. Aecidiospores were also 
sprayed on the shoots or injected into growing tips, leaf axils, etc. 
SPORIDIA ATOMIZED ON SHOOTS 
Aecidiospores were germinated on water in watch glasses, or on agar, 
and the sporidia thus obtained in large numbers were sprayed on the 
young shoots. It is clear that the use of sporidia instead of aecidiospores 
will prove to be more satisfactory in infection experiments since the 
time during which the plants must be kept in the damp chamber is 
shortened by at least 24 hours. In the writer's experiments, plants are 
