The Thallus of the genus Parmelia

In the ordinary works on Lichenology, the main object of the author is to give such a description of a species as will enable a student to determine a plant by himself, by examination of the thallus with a pocket lens, and of the apothecia and spores by the aid of a microscope.
The spermagonia and spermatia may be briefly referred to, but other matters are usually ignored. In this paper no reference will be made to a macroscopic study of the thallus, or to the histology of the apothecium, its paraphyses or spores.
In preparing the material for this paper, serial sections of the following lichens were cut, stained, and mounted for examination : Parmelia tiliacea, Ach., P. tinctorum, Despr., P, perlata, L., P.limbata, Laur., P. lara, M.A., P. perforata, Arch., P.latissima, Fee, P. placorhodioides, Nyl., P. mundata, Nyl., P. olivacea, L., P.cetrata v. sorediifera, Wain., and P. saxatilis v. signifera, M.A. —