Proceedings 27 
I feel convinced that a little patient field work would 
solve this problem. In the case of VP. cory/ea the field 
worker should search under trees attacked by PhyJlac- 
tinia for perithecia which have fallen off and become re- 
attached to leaves of the plants underneath. These leaves 
should be kept under observation, with the view of seeing 
if the ascospores really do escape from the dase of the 
perithecium, as we must suppose them to do. 
In the case of Uncinuda, it must be noted, we do not 
know what causes the perithecium to turn over, as, unlike 
Phyllactinia, it is certainly zo¢ caused by the appendages. 
The field worker should observe closely at the beginning 
of autumn the common Maple Mildew, Uncinula Aceris, 
very common on the maples in the hedges about here, 
The perithecia of this Maple Mildrew are very large, and 
therefore suitable for observation. The whole work could 
be done with a lens. Search should be made until some 
perithecia of this Maple Mildew are found turned over, 
The leaf should then be kept under close observation until 
the turning over of a perithecium is actually seen in Nature 
on the living leaf. The exact conditions under which the 
reversal took place should be carefully noted. 
The third question is: Do biologic species exist in the 
Lrysiphacee ? 
This problem is the most interesting one, on account 
of the bearing it has on several interesting scientific sub- 
jects, and also on account of its great economic importancea 
First, I must explain what mycologists mean by the term 
“biologic species.” 
About 1890, Dr. Jacob Eriksson, of Stockholm, made 
a number of careful experiments with certain parasitic 
fungi. These fungi belong to the genus Puccinza (of the 
Uredinee). They are parasitic on cereals, and are popu- 
larly known as “rusts.” 
Eriksson found that the rust growing on (say) Aye (al- 
though identical in all its characters, even to the shape, 
size, and marking of its spores, under the microscope, with 
the rust on Oa¢s) was not able to infect oats ; and con- 
a versely, the rust on oats could not infect rye. 
