1921] ADAMS~—BLISTER RUSTS 133 
I have examined specimens of Peridermium Strobi collected 
May 5 and 21, 1917, in New Hampshire by Dr. L. O. OverHotts. 
The specimens were in sporulating condition. In every instance 
the mature pycnial layer was found intact in the tissue overlying 
the aecia. Cottey also states that “the pycnia of Cronartium 
ribicola precede the aecia by at least one growing season on any 
given area of infection, and succeeding generations of pycnia and 
aecia follow a more or less definite schedule.”’ In this case the per- 
ennial infection is not restricted, as found with some other stem 
rusts. It is a typical progressive infection. The development of 
pycnia and aecia of the leaf rusts of conifers apparently is cor- 
related with the time of infection. In the case of Peridermium 
acicolum mature spermagonia have been found as early as March 1, 
and the aecial primordia developing May 25, 1917, only an inter- 
val of about three months intervening between the appearance of 
pycnia and aecia. The infection of the needles occurs the pre- 
ceding fall. Mature aecia of Peridermium Peckii were collected 
May 20, 1917, at Pine Grove Mills, Center County, Pennsylvania. 
The pycnia precede the aecia by two to three weeks, according to 
field observations. The same condition occurs in Coeoma A bietis- 
canadensis, which is found on the cones and new terminal growth 
of Tsuga canadensis. The infection with these two species occurs 
the same spring. These observations indicate that with respect 
to the seasonal interval there are at least three methods in the 
sequence of pycnia and aecia (or the completion of the gameto- 
phytic development on any given infected area). 
1. The first method is the alternation of pycnia and aecia in 
Peridermium cerebrum, as reported by Hepccock and Lone (7), and 
Donce and Apams (5). The evidence supports the contention that 
it takes two years to complete the gametophytic period of develop- 
ment on any given infected area. The pycnia appear in spring and 
are sloughed off about the middle or end of the same growing season. 
The following spring the aecia are developed. It is not until the 
third season that the pycnia again are developed. This condition 
may occur on the same gall, in which case apparently one part is 
an older infection. It is usually found that such areas represent 
different stages of maturity, and are differentiated by furrows. 
