Aug. 4, 1923 
Systemic Infections of Rubus with Orange-Rusts 
217 
periments the tip must have stopped growing forward or died, since in 
every case in which the tip grew beyond the rooted plantlet, it con¬ 
tained no mycelium. Certain stolons rooted early so that the shoots 
were of considerable size before teleutospores were available and were 
undoubtedly too old to become systemically infected. 
The experiments, described above by which tip plants were sys¬ 
temically infected were repeated during the summer of 1922. Teleuto¬ 
spores for this work were obtained from blackberry leaves. This attempt 
to infect the raspberry with the strain from blackberry proved successful; 
four of the tip plants showed orange-rust the next spring. 
FIEED EXPERIMENTS 
Leaves bearing teleutospores were laid over rooting tips of a number 
of wild raspberries in the field. The rainfall in this region was so limited 
in August and September, 1921, that these rooting tips rarely formed 
buds or shoots until the following spring. Only one plant was infected 
in this way. 
PRACTICAL CONSIDERATIONS 
PROPAGATION OP NEW PLANTS FROM DISEASED STOCK 
It is possible for an infected raspberry cane to become a stolon which 
by rooting will spread the disease to new plants in the nursery. The 
characteristic appearance in nature of plants heavily rusted suggests that 
this is not a common occurrence because so many infected canes are of 
the broom type, short and spindling; and it is well known that the 
entire plant frequently dies from the effect of the rust. On the other 
hand, as noted previously, rusted canes may recover their vigor and 
many shoots which arise late in the season do not, of course, show any 
outbreak of the rust. Several rusted raspberries in nature and in the 
greenhouse were observed in 1921 and later. In many of these no stolons 
were formed, but occasionally canes clearly diseased did take root at 
the tips and gave rise to new plants. In several such cases the rooted 
plants were cut away from the parents and pieces of the stolons were 
sectioned. It was found in each case that the mycelium was present 
in the pith of the cane which had rooted at the tips, and that it must 
have entered the buds from which the new plants developed because 
they showed the rust the following spring. 
RUST-FREE PLANTS FROM INFECTED STOCK 
One commonly observes that some young canes in an infected hill do 
not show rust. When no mycelium can be found in such canes, it is 
clear that they arise from a part of the crown into which the fungus has 
not penetrated. These canes taking root at the tips must give rise to 
perfectly healthy plants. An infected plant was brought from Massachu¬ 
setts, in June, 1920. A stolon was formed after the plant had apparently 
recovered from the rust. This stolon was examined after it had taken 
root at the tip, but no mycelium was found. The new tip plant showed 
no rust in 1921. It would be bad practice in a nursery to use such plants 
for stock, because, as noted above, mycelium may exist in a cane which 
shows no signs of the rust at the time. New plants arising from rooting 
stolons may be readily infected in August and September, but if the tip 
