Further studies of the orange rusts of Rubus in the United States 
L. O. KUNKEL 
(WITH FIVE TEXT FIGURES) 
INTRODUCTION 
The writer’s previousstudies of the orange rust, showing that the 
Caeoma spores in material from New York, Illinois, Missouri and 
Wisconsin (6, 7) germinate like teleutospores, left the question 
as to the relationships of Puccinia Peckiana Howe unsolved. 
Fischer (5) has recently tested the germination of the aecidio- 
spores of the European Gymnoconia interstitialis (Schlecht.) Lagerh. 
He obtained long germ tubes having all the characteristics of 
ordinary aecidiospore germ tubes. No promycelia were observed 
and no cross walls were to be seen in any of the tubes. In one 
case a thinner tube that resembled somewhat a long sterigma 
developed at the end of a germ tube. This he thinks may have 
been the result of growth disturbances. Fischer also made infec- 
tion experiments and obtained Puccinia Peckiana by sowing the 
aecidiospores on supposedly healthy plants of Rubus saxatilis. 
His results, taken in connection with those of Tranzschel (13), 
Clinton (3), and Liro (9), give strong evidence in favor of the 
view that Caeoma interstitiale Schlecht. and Puccinia Peckiana 
are connected. Fischer (5) explains the seeming contradiction 
between his results and those of the writer by assuming that we 
have been working with two different fungi. According to this 
view there would be two orange rusts on the blackberries of 
America: one the aecidial stage of Gymnoconia interstitialis, the 
other a short-cycled rust closely related to the genus Endophyllum. 
So far as known the short-cycled rust, which we may refer to 
under the name Caeoma nitens Burrill, does not occur in Europe. 
The fact that there, both are limited to the same low-growing wild 
species of Rubus is evidence in favor of such an assumption. 
Puccinia Peckiana, however, is not uncommon in several different 
parts of America, and we must expect to find its aecidial stage in 
these localities. 
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