138 MISSOURI BOTANICAL GARDEN, 
farinacea, they are unaccompanied by marked morpho- 
logical or structural differences, it seems decidedly unwise 
to employ them alone for the establishment of species. If 
the tests be made under the microscope, it will be seen at 
once that only those with iodine affect the actual lichen 
tissue—the others affecting only excreted or extraneous 
matter. Though the former can be considered perhaps a 
part of the lichen, as much as the waxy excretion of the 
phanerogamic glaucous leaf, yet it is hardly an important 
structural indication of differentiation. Again, it is well- 
known that certain lichen acids which are the cause of 
these color reactions (potash with atranoric acid, etc.), are 
developed occasionally only in young thalli growing on 
certain substrata (i. e., Xanthorina parietina on sandstone), 
and such “considerations should make one very wary in 
placing reliance on these color reactions for the purposes of 
classification.’ 
SYNONYMY. 
As the complete and accurate synonymy of a large number 
of lichens is impossible to compile (1. ¢. 6), a comparison of 
all types being necessary, I am giving here only the “name 
finding” synonymy and any other titles which have been 
used to designate the species in North American works. 
These I have included only when absolutely sure of their 
synonymous character. 
NOMENCLATURE. 
The International Botanical Code has been followed. I 
have indicated, however, the type species of each genus. No 
forms, states or phases are recognized by title. Much 
lichenological nomenclature can hardly be termed binomial. 
TYPE MATERIAL. 
One of the most important portions of my work on this 
family has been the investigation of types, photographs of 
which accompany the species here described. In my former 
