Arthur and Kern: North American Peridermium 113 
ing teliospores are inserted into a slit in the bark of the pine, care 
being taken to include as little debris as possible and to keep the 
surface moist for some hours. 
The basidiospores both in Coleosporium and Cronartium are 
ready to be shed immediately upon maturity of the telia, which is 
largely from July to late fall. The earlier maturing telia are 
likely to give best results. Some indications of success may occa- 
sionally be seen after a few weeks, but the aecia are not likely to 
appear until the following spring. 
Reverse cultures may similarly be made by suspending leaves 
or bark of pine, bearing the aecia, over the suspected alternate 
host, usually low growing herbs. Such work must largely be done 
in spring; and the first mature aecia from such cultures may be 
again used, and provide more viable spores than those gathered in 
the field. The uredinia that result from aecial infection will prob- 
ably appear within ten to thirty days, usually on the under side of 
the leaves. 
Herbarium specimens should invariably be saved, both of the 
material from which sowings are made, and of the resulting spore 
forms. 
In the present stage of knowledge there is needed a large 
amount of work on the microscopic characters of the collections 
now in herbaria. It not infrequently happens that two collections 
having similar gross appearance present well marked microscopic 
differences. Or it may be that two specimens with dissimilar 
gross appearance, as P. cerebrum and P. fnsiforme, now known 
to be one species, have no material microscopic differences, when 
well studied. A certain amount of variation in all the microscopic 
characters must be expected, in some species more than in others. 
The extent of this variation in each species can only be ascertained 
by extended microscopic study of large numbers of authenticated 
collections made at different times and places. Although more 
characters are now utilized than formerly, especially those per- 
taining to the peridium, and better technique employed, yet it is 
not likely that all species can be definitely separated by micro- 
scopic characters alone. Especially among those species of Peri- 
dermium which are aecial forms of Coleosporium, that is, the 
foliicolous forms, there is frequently great similarity. But even 
