230 
Journal o} Agricultural Research 
Vol. XXV, No. 5 
closely connected with the original crown. Can these new shoots be 
infected in such a way that the rust becomes established in a plant, the 
underground parts of which may be several years old? Plant No. 24 
(see p. 225), was derived from a wild blackberry crown, potted February 
14, 1921. The shoot was infected so near its top that the fungus was 
unable to reach the underground organs, whereas, if the parasite had 
entered the shoot when it was just emerging from the soil or at its lowest 
nodes, hyphae could have penetrated into the underground parts and 
become firmly established. In some of our experiments shoots from the 
old underground stem were sprayed with sporidia along with the root 
shoots. In two instances these shoots became infected. The infection 
of old crowns, however, by the rust is probably a rare occurrence in 
nature. When this occurs there will be for several years a number of 
healthy canes in this hill with only one or two canes showing rust, where¬ 
as if the nursary stock or a root shoot is infected the hill derived from 
either will be worthless from the beginning. 
MYCEUUM FROM A PRIMARY INFECTION IN THE GROWING REGION OF THE CANE 
Emphasis has been laid upon the point that, in a large percentage of 
cases observed in our work, the mycelium developing after an inocula¬ 
tion of shoots with sporidia does not travel to any extent up the cane 
as it grows, but tends to make its way downward into the underground 
organs, with the result that in the following spring, leaves on new shoots 
from the base of the cane originally infected and leaves at a few' of the 
basal nodes will develop aecidia, while the cane throughout its upper 
portion is perfectly normal, bearing blossoms. No mycelium will be 
found in any of its tissues, except, of course, in the immediate region 
of the lower rust-bearing leaves. A few notable exceptions to this 
general rule have been observed. Old canes or branches clearly proved 
to have been infected as the result of inoculation showed symptoms of 
having been systemically infected throughout their entire length. 
Sections of the canes showed mycelium confined to the pith, except at 
the nodes, just as in canes secondarily infected. Their appearance is 
quite characteristic, owing to the proliferating terminal and axial buds. 
Why the fungus behaves in this exceptional way is not clear. No. 135 
may be taken as an example of this type of infection. The plant 
originated as a root shoot from a Kittatinny blackberry 2 feet away. 
The parent plant has shown no rust for three years. The shoot was 
about 1 foot high when inoculated with aecidiospores May 23, 1921. 
On September 28 it was noted that a branch from the base of the plant 
appeared somewhat abnormal, as though it might be infected. On 
April 28, the following spring, pycnia appeared on the leaves of the 
new shoots. On May 8 the infected plant, including the entire root 
system back to the parent plant, was dug up. The plant now consisted 
of one large 1921 cane which had been broken off 14 inches above the 
soil during the preceding summer. Leaves at the basal nodes were 
rusted and three large new shoots from its base had developed; to this 
extent the infection appeared to be typical. There was, however, 
one large 1921 cane (a branch from the lowest node of the cane originally 
inoculated) which showed peculiarities in that several of its axial buds 
had been stimulated to grow out into new shoots (PI. 6, b) and the 
terminal bud of the 1921 cane had also grown out into a long new shoot, 
a. This certainly is exceptional behavior for our blackberry, whose 
