zoids are quite numerous. The apothecial and spore characters are 

 taken from P. picta, P. sorediata being, to my knowledge, always 

 sterile. They are in most respects similar to those of the higher 

 forms of JRtnodma; the paraphyses are shorter and the spores are 

 comparatively few in number * the dark hypothecium is semi-cortical 

 in structure ; the hyphae everywhere contain large deposits of crys- 

 tals of lichen-acid. In the thallus of P. picta the upper cortical 

 tissue is deficient ; the lower is wholly wanting, its place being taken 

 by a network of hyphae with dark-colored cell-walls. 



The thallus of P. sorediata is more highly developed than that 

 of P. -picta; it bears numerous soredia upon the upper surface of 

 the thallus, as well as along the margin. Apothecia never occur ; 

 propagation in this species being entirely dependent upon the soredia. 



P. ptcta seems to be southern in its range, w r hile P. sorediata is 

 more northern ; both occur upon bark and rotten logs. 



PLATE 36. 

 PYXINE PICTA (Sw.) Tuck. 



1. Portion of thallus, natural size. 



2. Section of apothecium. 



3. Section of thallus. 



4. Paraphyses and spore-sac. 



5. Spores. 



6. Algae. 



4. PHYSCIA Schreb. Gen. 2: 768. 1791. 



The thallus of Physcia presents all gradations from nearly crus- 

 taceous (P. adglutinata), through foliose (P. stellaris and the ma- 

 jority of species) to fruticose (P. ciliaris, P. leucomela} . The gen- 

 eral characters of P. adghitinata indicate the close relationship of 

 Physcia to Rinodina, from which genus it is doubtless phylogenetic- 

 ally derived. In the majority of the representatives of this genus 

 the thallus is typically foliose with the various tissue-layers well 

 differentiated. The cortical tissue, however, differs considerably 

 from that of Parmelia and the majority of foliose lichens, con- 

 sisting of rather short, much interwoven, closely united hyphal 

 branches, and the walls of the hvphal cells are considerably thick- 

 ened and gelatinized ; intercellular spaces are rare and the cell-lu- 

 mina are much reduced. Rhizoids are numerous and well developed. 



