GAMETOPHYTIC DEVELOPMENT OF BLISTER RUSTS' 
J. F. ADAMS 
(WITH FOUR FIGURES) 
Since the discovery of the pycnial stages for the stem forms of 
blister rusts on pines, several interesting points have arisen with 
respect to their alternation with the aecial stage. The pycnial 
stage of rusts on Angiosperms usually precedes the appearance of 
the subsequent stage (aecia, primary uredinia, or telia) by a few 
days to several weeks. The interval of time in completing the 
gametophytic development in the case of the stem rusts on pines 
is materially different. 
WEIR and Husert (9) have added much to our knowledge 
regarding the appearance of pycnia of several blister rusts. Pycnia 
of Cronartium cerebrum on Pinus Banksiana were collected as 
early as May 12, 1916. Four of the galls developed aecia within 
4 or 5mm. from the pycnial exudations on the same galls, but not 
from identical pycnial areas. The pycniospores of C. Compioniae 
developed similarly to those of C. Comandrae in respect to their 
appearance on previously unruptured tissue. They secured exuda- 
tion of pycniospores by laboratory forcing methods from specimens 
collected on May 12, 1916, at Cass Lake, Minnesota. They report 
as follows: 
In Cronartium coleosporoides the pycniospores are er e a galls 
previously ruptured, as well as on unruptured infected tissues . period 
from April 4 to 15, 1916, abundant pycnial exudations compatnina ei pycniospo: 
were obtained from galls of C. coleosporoides .... The pycniospores of 
C. Comandrae apparently develop but once on the same tissue preceding the 
appearance of the aeciospores. The production of aecia kills the infected 
tissues which are included in the aecial ruptures. The tissues bordering this 
area are invaded by the mycelium of the fungus, produce swellings, and give 
rise to pycniospores, either in early spring or in late summer and fall, whenever 
sufficient time has elapsed from the last production of aecia. In the cases 
recorded the pycniospores appeared in the same season following the production 
of aecia, with only five months intervening, but not from the identical area 
from which the pycnia were produced. 
* Contribution from the Department of Botany, The Pennsylvania State College, 
a Oi 
131] [Botanical Gazette, vol. 71 
