1914] 



BURT — THELEPHORACE^ OF NORTH AMERICA. I 191 



Probably all species of Corticimn, as originally understood, 

 have an hymenium composed of basidia arranged side by side 

 between non-sporebearing organs termed paraphyses. In many 

 species, it is difficult to distinguish between the basidia and 

 the paraphyses except by prolonged study of special prepa- 

 rations or by observations made at the time the basidia bear 

 spores. In other species the sterile organs are conspicuous and 

 distinct from the basidia either by their larger size, different 

 form, or thicker or incrusted walls. Such conspicuous bodies 

 are called cystidia, but if the paraphyses are merely finely but 

 characteristically branched near their tips, they are not called 

 cystidia. Such branched paraphyses occur in the hymenium 

 of occasional species of several genera of the Thelephoracece and 

 are valuable characters for specific diagnosis. 



In 1880, Cooke proposed, from Kew Herbarium, to divide 

 the old genus Corticium into two genera, — the name Corticium 

 to be retained for those species having the non-sporebearing 

 organs of the hymenium not distinguishable from the basidia, 

 and the generic name Peniophora to be given to those species 

 having cystidia. As the species of Corticium were very num- 

 erous and extremely difficult taxonomically, this proposal was 

 hopefully received, and for more than thirty years the transfer 

 of species from Corticium to Peniophora has been going on and 

 the end has not been reached yet. During this long period 

 there has been confusion as to which species of the old genus 

 Corticium belong in the emended Corticium and which in the 

 genus Peniophora. 



Peniophora is an artificial rather than a natural genus, how- 

 ever, and its adoption has given to many species a position 

 intermediate between this genus and Corticium. These inter- 

 mediate species have to be classed with the one genus or the 

 other according to personal judgment, for no one can state just 

 how conspicuous the sterile organs must be, nor of how constant 

 occurrence, to merit the name cystidia. In Corticium Sambuci 

 Ft., for example, cystidia are readily found in preparations from 

 some collections, but several preparations may have to be made 

 to demonstrate them in other collections. In the same species 

 and in different parts of the same section, cystidia may some- 

 times be sparingly and sometimes not at all incrusted. Some 



