June i 6 , IQ23 
Pucciniastrtim americanum 
887 
An inspection of the berries grown at the Government farm at Arling- 
ton, Va., was not made until the latter part of September. From 6 to 
50 hills each of Cuthbert, King, Ranere, Antwerp, wild Rubus occidentalism 
Kansas, Black Pearl, Cumberland, Plum Farmer, Shaffer, Columbian, 
and Royal Purple are grown. The Cuthbert red raspberry was the most 
severely attacked; much defoliation had resulted, and the remaining 
lower leaves were well covered with uredinia. Considerable rust was 
found on the Columbian, Royal Purple, and the Victor. The Ranere 
(St. Regis) and King varieties bore some rust, but not enough to cause 
any damage. No rust was found on any of the black raspberries grown 
here, and as R. occidentalis (at Bell, Md.) showed no rust it may be as¬ 
sumed that our black raspberries are very resistant. It is not strange to 
find that crosses between the black and the red varieties in many cases 
prove to be very susceptible. Whether the strain of the rust which 
made its appearance in the vicinity of Washington, D. C., is more viru¬ 
lent than that heretofore found on Rubus ''neglectus'' and R, strigosus is 
not known, but it is evident that many of the hybrids at Bell are more 
susceptible than either of the parents. 
The host is occasionally erroneously identified by collectors, especially 
in the case of the red raspberry, which is often confused with the black 
raspberry. For example, in the Path. Coll., B. P. I., is found No. 2280, 
N. A. Uredinales, one gathering at Madison, Wis., October 6, 1906, and 
another at Mackinac, Mich., September 6, 1894, which the host is 
given as R. occidentalis when it is a red raspberry. Arthur (2, p. igo) 
states that R. occidentalis was erroneously given as a host for Puccini- 
astrum americanum in Bull. Torrey Club (j, p. 468). In the same article 
a specimen from Algoma, Wis., was referred to P. arcticumm and the host 
is given as R. occidentalis. ff^he rust is clearly of the P. americanum 
type, and the host is R. strigosus. Davis (6) has shown that R. occidentalis 
can be infected by P. americanum from R. strigosus. We have not found 
pustules of this rust on the wild black raspberry in the vicinity of Wash¬ 
ington, D. C., but more careful search would very likely result success¬ 
fully. The rust is undoubtedly more widely distributed than is com-/ 
monly supposed. Specimens on cultivated raspberries have been referred 
to other species by mistake. In the Path. Coll., B. P. I., we find one 
packet of the rust on a red raspberry originally labeled Lecythea Ruborum 
Lev.; No. 32, Economic Fungi, Seymour and Earle, Phragmidium 
Rubi-Idaei (P) Wint. is Pucciniastrum americanum. One gathering of 
Pucciniastrum on R. strigosus was sent to the author as orange-rust 
in response to a request for red raspberry plants infected with the 
Gymnoconia. 
THE MORPHOLOGY OF THE UREDINIUM 
Farlow (9) recognized that the rust which he had found on a hybrid 
raspberry differed somewhat with respect to the shape of the peridium 
from Pucciniastrum arcticum of Europe. The peridium was more sharply 
conical than that of P. arcticum^ which is said tp be low and broad. He 
called attention to a good illustration of the peridium of the American form 
by Dietel in Hedwigia (7, p. jji) under the name Phragmidium gracile. 
Farlow proposed the variety name americanum^ which Arthur (j, p. 468) 
later raised to specific rank. Davis (5) has shown that Pucciniastrum 
arcticum is very common in Wisconsin on Rubus triflorus and questioned 
at that time whether the differences in the morphology noted by Farlow 
may not after all be due to host differences. He is now convinced (6), 
