220 
Journal of Agricultural Research 
Vol. XXV, No. 5 
kept under the infection frame two days when sporidia are used, and three 
or four days when aecidiospores are sowed. 
INOCULATION BY MEANS OF THE HYPODERMIC NEEDLE 
A number of attempts were made to infect young shoots by injecting 
spores into their growing tips with a hypodermic needle. In several 
cases infection followed in spite of, rather than because of, this method. 
The needle was loaded with an abundance of sporidia and generous doses 
were given the young shoots. Water containing sporidia must have 
trickled from the wounds over the surface of the young shoots, which 
were exposed by digging away the surrounding soil. The injury to the 
growing tips manifested itself the following year. The ends which had 
been punctured usually died and new shoots developed from below. 
INOCULATION IN THE OPEN 
During rainy weather when the plants remained moist for the greater 
part of a day or two, inoculations were made with great success by 
spraying young shoots with sporidia without the use of artificial methods 
for maintaining the humidity. These experiments were conducted some¬ 
what apart from those which were more nearly under control through 
the use of muslin infection frames. 
CONTROLS 
For reasons which will be made clear later, definite control plants were 
not set aside in this work, although all plants of the same horticultural 
variety in near-by hills could be considered as control plants, especially 
where no damp chambers were used. Plants in well-cultivated fields do 
not serve well as controls since so many of the young shoots are inten¬ 
tionally destroyed in cultivating, and these young plants would be the 
ones most readily infected by spores from wild blackberries in the 
vicinity. The destruction of the young shoots that grew up between the 
hills and rows in the field was avoided in order that use might be 
made of as many of them as possible as an additional check on 
the results. Most of the infection experiments with blackberries for 
1921 were made in the field plots where exposure to natural infection 
must be taken into consideration, and it should be remembered that 
greenhouse conditions in this regard are only slightly more dependable in 
a region where the orange-rust is so common that vast numbers of spores 
are very likely to be blown into the ventilators of a greenhouse. One 
can not be quite certain, therefore, in this vicinity that any particular 
plant may not have been infected by these wind-borne spores. 
It has been shown previously how the rust may be carried from plant 
to plant through the root runners, so in a group of wild blackberries in 
which a large number of the plants are rusted it may be that the number 
of infected plants had increased year by year, as roots containing my¬ 
celium gave rise to new shoots. A single primary infection might easily 
account in this way for conditions where nearly every plant in a stand 
of wild berries is rusted. Therefore, as an additional safeguard after 
the writer's plants had been received from nurseries during April and 
May, 1920, and also in 1921 when the first inoculation work was done, a 
careful inspection was made from day to day. The work was, therefore, 
begun with plants whose canes showed no rust the first and second 
seasons of their growth. For example, a stock plant set out in 1920 
