Jan. 1907] The Genus Cortinarius , with Key 33 



not be too full, provided they contain the essential facts mentioned 

 first." (Bulletin of the Torrey Botanical Club.) 



THE KEY. 



The key which is here presented is a revision, with many 

 additions, of the key printed in the Bulletin of the Torrey Botan- 

 ical Club, June, 1905. It is based on the study of fresh plants ; 

 but there have been added a few which the writer has not seen, 

 but which have characters so easily recognized, and so different 

 from others, that they were thought worthy of inclusion. This 

 key, like its predecessor, necessarily has many shortcomings. As 

 long as we are not sure what American plants are really identical 

 with European ones, and so long as good figures or photographs 

 of the species described for North America, are lacking, we are 

 easily able to mistake the meanings of the descriptions, which are 

 often of the very briefest. Hence this list is merely offered as a 

 slight forward step towards opening up for amateurs the study 

 of this interesting genus. 



Six species, which the writer believes to be undescribed, 

 have been included, although their descriptions have not yet been 

 published. All of them have been collected or been received from 

 various places more than once, and by inserting them in the key, 

 we may be able to help those who continue to come across them. 

 It is hoped soon to publish descriptions of them elsewhere. 



It is to be noted that the key has been built largely on the 

 size of the spores. This will necessitate, it is hoped, the study 

 of the plant under the microscope, and so initiate the beginner 

 at once into the proper study of these fungi. We know that two 

 different species of mushrooms have again and again been placed 

 under one name because of similar external appearances, when 

 an examination of the spores would have shown a difference of 

 as much as 8 microns in some cases. In deciding on the size 

 of spores, the measurement of mature spores only should be taken, 

 which may be recognized by the dark wall or the roughness of the 

 exospore ; even in plants with yellowish spores a difference be- 

 tween young and mature spores can be made out. 



KEY TO THE COMMON SPECIES OF CORTINARIUS OF EASTERN 

 NORTH AMERICA. 



A. Pileus with a gelatinous cuticle, more or less viscid or 

 glutinous M^hen moist, as is also the stem in some species. 

 [Myxacium and Phlegmacium.] 



a. Pileus coarsely corrugate C. corrugatus Pk. 



