A METHOD OF DETERMINING IN ANALYTIC 
WORK WHETHER COLONIES OF THE 
CHESTNUT BLIGHT FUNGUS ORIG- 
INATE FROM PYCNOSPORES 
OR ASCOSPORES^ 
F. D. Heald 
(With Plates 98-101) 
Introduction 
In studying the dissemination of the chestnut-tree blight fun- 
gus [Endothia parasitica (Murr.) x\nd. and And.] it is sometimes 
of importance to be able to determine whether the colonies of 
Endothia appearing in poured plates originate from pycnospores 
or ascospores. This is especially true in case of the analysis of 
soil for the presence of the fungus, the quantitative determination 
of viable spores retained in spore traps, and other similar 
operations. 
During the past winter thousands of cultures of the blight 
fungus have been made, especially in studying the problem of dis- 
semination, but before beginning the work the method here out- 
lined was worked out, as it appeared to the writer of fundamental 
importance. 
At first thought the possibility of differentiating ascospore and 
pycnospore colonies seemed somewhat remote, but the striking 
difference in size of pycnospores and ascospores offered the first 
clue to the problem. The approximate dimension of the spores 
(ascospores 5X10/^; pycnospores iX 3 - 5 m) gives rather an 
imperfect notion of their difference in magnitude, but calculation 
will show that the ascospore of average size has a volume about 
fifty times that of the average pycnospore. It seemed evident 
then that the greater size of the ascospore would result in a more 
rapid growth of the colonies originating from them. 
1 Work in cooperation with the Pennsylvania Chestnut-Tree Blight Com- 
mission, Philadelphia, Pa. 
274 
