134 BOTANICAL GAZETTE [FEBRUARY 
Whether the form of Peridermium cerebrum is the same as P. 
giganteum remains to be established. Surrar describes as well as 
illustrates the pycnia in the tissue overlying the aecia, which would 
not agree with our observations on the American form. It is 
possible that environmental conditions may be concerned in this 
instance. 
2. The second method is that in which maturity of the pycnia 
precedes the aecia in adjacent as well as the overlying tissue within 
a period of about six months. The full cycle of development of 
pycnia and aecia on the coniferous host in the same area is com-- 
pleted within a period of twelve months. In contrast with the 
first method the pycnia and aecia are sloughed off at the same 
time. The writer (1) has shown that the pycnia occur in the 
tissue overlying the aecia in Peridermium Comptoniae and P. pyri- 
forme. Being sloughed off at the same time indicates there is no 
alternation as found with P. cerebrum. It was not known when 
the pycnia developed, since the exudation of pycniospores was 
never observed in the field when this material was collected. The 
presence of the pycnial layer, however, could be recognized by 
carefully removing the bark. At this time the pycnia appeared 
as an extensive olive green layer, irregular in outline, and mature. 
On October 17, 1919, in the vicinity of State College several infec- 
tions of Peridermium Comptoniae on Pinus virginiana were observed 
with exudations of pycniospores. Their appearance was similar to 
the description given by WeErr and Husert. On removing the 
bark the pycnial layer was lemon yellow in color. Cross-sections 
showed the usual extensive crustlike layer of the pycnia. There 
were extensive pycnial primordia which indicate the immature 
development of the pycnial layer. From these observations and 
others it would appear that P. Comptoniae, P. pyriforme, P. coleo- 
sporoides, and P. Strobi represent a group of species in which the 
pycnia and aecia complete their period of development within twelve 
months. No doubt certain environments or other conditions may 
alternate the period of time the pycnia may appear in one season, 
but it seems probable that this sequence is more or less regular 
after the first period of development has been completed. The 
completion of the initial gametophytic period of development 
