Notes on some North American species of Parmelia. 
HENRY WILLEY. 
younger of the two. Specimens gathered at other timés 
yielded no reaction. The cladonias also present similar diff- 
culties. It is possible that a lichen may possess different 
chemical constituents at different stages of growth, or u® ie 
different conditions of soil, climate, etc. Experiment on i 
pears to be an exception we may best say that ‘‘perhaps 
uckerman, Whose views in regard to species were Ve 
conservative, described in his Synopsis nineteen nae 
Parmelia. ome of his varieties are regarded by other au! Ny 
either on chemical or other grounds, as distinct spect¢> 
[202] 
