232 
Journal of Agricultural Research 
Vol. XXV, No. S 
EFFECT OF INJURY TO THE GROWING POINT 
Very frequently when the hypodermic needle is used to inoculate the 
growing point of a shoot, the injury leads to the death of the end 
punctured. Sometimes when the soil is being removed from around the 
root sprouts, the ends will be broken off so that the effect on their future 
development is practically the same. A new shoot immediately grows 
out from an axial bud below. The following spring the cane into which 
the shoot develops will have a short right-angled bend at the point where 
the scar tissue healed over the end-portion which had died. The plant 
shown in Plate 4, B, a, also illustrates this feature. On May 5, 1921, 
the soil was dug up around a plant of the Iceberg variety so that three 
shoots about 2 inches long were exposed. No. 112 A was inoculated by 
injecting sporidia into the growing point and spraying them over the 
surface; aecidiospores were also dusted over the young plant, with the 
hope that one or the other method might result in infection. No. 112 B 
and 112 C were merely sprayed with sporidia. The growing point of 
the first plant which had been injured died, and three new shoots grew 
out soon after from axial buds below. One of these became the leader 
and also gave rise to a secondary branch. The leader grew to be 5 feet 
high and blossomed normally the next year. Leaves at the lower nodes 
bore the orange-rust May 3,1922. Four new shoots, systemically infected, 
now arose from the base of the main cane, but its 1921 branch, as well as 
the other two canes that were developed in 1921, as noted, showed no rust. 
The mycelium apparently had not penetrated the horizontal root to any 
extent, as there were no shoots or buds on the root such as one finds when 
it is infected. It was found that this root had also given rise in 1921 to 
the shoot 112 B, mentioned above. Infection resulted from spraying 
sporidia on the shoot. In May, 1922, it consisted of a single old cane bear¬ 
ing an abundance of blossoms, and the leaves only at the lowest nodes were 
rusted. New shoots, bearing pycnia were springing up from that part 
of the cane beneath the soil. 
When plants A and B are compared it is seen that the result of killing 
the growing tip of the inoculated shoot in plant A was simply to stimulate 
the axial buds to grow into new branches at once, but the type of infection 
in this case was not altered thereby. Anything that stimulates the 
development of new and therefore more susceptible shoots or branches 
from time to time throughout the,period of spore dispersal, which varies 
from two weeks to a month or over, increases the chances of infection 
proportionately. Very striking effects of accidental layering of Rubus 
enslenii in a neglected cemetery at Winston-Salem, N. C., were observed 
in April, 1922. A number of graves had been dug the preceding year and 
the dirt thrown out over these wild dewberry vines. The following spring 
practically every shoot that was found growing through the covering of 
dirt from the excavations was rusted. Very few rusted plants were 
found in this cemetery where the vines had not been disturbed or covered. 
ROOTS SUSCEPTIBLE TO INFECTION 
One frequently finds orange-rust in hedge rows along the margins of 
cultivated fields, along embankments, or in pastures, where injury to 
the canes and roots is very likely to occur. This has suggested the 
possibility that the blackberry may also be primarily infected through 
its roots which become exposed through cultivation or otherwise. A 
few cases of infection were found in the writer’s work which were difficult 
