Arthur and Kern : North American Peridermium 131 
in this country if every precaution is not taken to stamp out the 
disease. Recently the rust has been found fully established on 
large trees of native white pine in northern Vermont. Steps 
have been taken to extirpate it in this locality. The quarantine 
regulations of the various states and of the federal government 
are clearly efforts in the right direction. It may be found neces- 
sary eventually to prohibit importation of white pine stock. 
Since 1909, and possibly earlier, the presence of a Cronartium 
on Ribcs longiflorum has been known from Colorado through the 
collections of Mr. E. Bethel. The rust has been especially com- 
mon in the parks of Denver and Boulder, and has appeared each 
year in the same spots since the first observation, but does not 
seem to have spread. Search at different times by Mr. Bethel has 
failed to reveal any aecial source of the infection. No white 
pines, or other species of pine which could be suspected of har- 
boring the rust, grow in the immediate vicinity. A careful search 
was made at the Boulder station in August, 1911, by the writers 
aided by Mr. Bethel, and again in August, 1912, by the senior 
writer alone, but no additional evidence could be detected to ex- 
plain the outbreak. 
15. Peridermium Comptoniae (Arthur) Orton & Adams, 
Phytopath. 4 : 24. 1914 
Cronartium Comptoniae Arth. Bull. Torrey Club 33: 29. 1906. 
Peridermium pyriforme [Peck, misapplied by] Arth. & Kern, 
Bull. Torrey Club 33 : 419. 1906. 
0. Pycnia unknown. 
1. Aecia chiefly on small branches 0.5-2 cm. in diameter, or on 
the trunks of small trees 2.5-5 cm - i n diameter, producing only 
slight fusiform enlargements, individual sori rounded or irregular, 
1— 1.5 by 1-2 mm. across, sometimes larger by becoming confluent, 
subhemispherical, 1-2 mm. high, rupturing irregularly along the 
sides; aeciospores ellipsoid or obovate, 16-24x24-33 n; wall 
2.5-4 fi thick, rather coarsely verrucose with irregular and some- 
what deciduous tubercles, with a smooth area at base often ex- 
tending up one side. 
On Pinus austriaca Hoss., Connecticut ( Clinton , see Rep. Conn. 
Exp. Sta. for 1912, p. 354). 
