1921] ADAMS—BLISTER RUSTS 135 
appears to be variable. CLINTON (3, 4) has shown, by infection of 
white pines with telia of Cronartium ribicola, that the pycnia may 
appear with the initial infection after a period of six months, one 
year, two years, and sometimes three years. 
3. The third method is found with the leaf rusts of conifers 
when the period of development is completed within one growing 
season. This is similar to the period of pycnial and aecial develop- 
Oe 
a o on 
KY) | SOS 
aL , oo is yy 
fly | oe 
=. — att 
Fic. 1 Fic. 2 
Fics, 1, 2—Fig. 1, cross-section of pycnial layer of Peridermium Comptoniae 
on Pinus virginiana; fig. 2, cross-section of pycnial layer of D etcieres cerebrum 
on Pinus rigida; drawn with camera lucida at same magnificatio: 
ment of Angiosperms. I have found mature pycnia of Perider- 
mium acicolum March 1, 1917, at Pine Grove Mills, Center County, 
Pennsylvania, while mature aecia were collected May 25, 1917. 
In the case of P. Peckii the pycnia were observed to precede the 
aecia by only two or three weeks; this difference may be correlated 
with the time of infection. With P. acicolum infection occurs in 
the fall; while with P. Peckii infection occurs after the new growth 
is developed in the spring. 
