234 
Journal of Agricultural Research 
Vol. XXV, No. S 
free from rust May 5, 1922, was found attached to the horizontal root 
6 inches from the parent crown. Sixteen inches beyond, infected shoots 
were vigorously developing. Sections of the root at x, y, and z were 
made but no hyphae were present at these points. No old cane nor any 
remains of such could be found among the new shoots. There was, 
however, a very definite scar tissue partially covering an old wound, 
at w, about an inch long. The root at this point was, when dug, not 
buried over one-half an inch in the soil, as is clear from the photograph. 
I do not doubt in the least that the root was originally infected in this 
wounded tissue. 
INFECTION OF BLACKBERRIES IN THE GREENHOUSE 
For reasons previously stated, very little work was done in 1921 in at¬ 
tempting to infect blackberries in the greenhouse. As the rust can cer¬ 
tainly remain alive in the crown and roots of a plant at least a year without 
appearing in the canes, one is not certain that his plant, brought in from 
nature, may not be infected. Such plants should be observed two or 
three years before being used for experimental purposes, no matter how 
many controls are used. On the other hand, by careful investigation of 
the distribution of the mycelium in various structures of an infected plant, 
one need not remain in doubt, in most cases, as to the time his plant 
became infected. For example, if mycelium is found in the pith of an old 
cane whose leaves are rusted the spring following inoculation, it is pretty 
good evidence that the fungus was present in the plant at the beginning, 
but if hyphae are found in the phloem, near the outer ends of themedullary 
rays, or along the cambium or in the cortex, but not in the pith, this will 
be very good evidence that this cane was infected through inoculation 
with spores. Only in rare cases does the rust establish itself in the grow¬ 
ing point at the time of primary infection. This does sometimes happen, 
as noted elsewhere, but such cases are very characteristic in their growth 
the spring following. In the spring of 1922, a number of blackberry 
shoots growing in “ flats ” were inoculated with the short-cycled rust. 
As sections of canes which developed rust the following spring showed 
no hyphae in the central pith, it is evident that the infections were 
primary and the result of the inoculation. 
PRIMARY AND SECONDARY SYSTEMIC INFECTIONS CONTRASTED 
Plants set out in the benches or in large “flats” make root shoots at 
some distance from the parent plant, but they are not very satisfactory 
for these experiments. Twelve root shoots of rust-free Kittatinny black¬ 
berries were planted in “flats” in the greenhouse April 13, 1922. By 
May 29 new canes had grown to be from 6 inches to 2 feet high. In order 
to determine whether canes of such a size could be infected systemically, 
they were sprayed at this time with aecidiospores of the short-cycled 
rust from a wild blackberry, and kept in the damp chamber three days. 
Having been overwintered in the cold frame, they were brought back to 
the greenhouse March 10. Leaves soon appeared on the old canes which 
had been inoculated, as noted, the previous year, and new shoots began 
to grow up from the base of the canes. For at least two weeks all leaves 
formed were perfectly normal, dark green, hairy on both sides, and not 
dwarfed. There was nothing abnormal in the appearance of the canes. 
About March 24 the latest leaves just unfolding at certain nodes became 
yellowish-green at the margins, which were more finely lobed and wrin- 
