408 Arthur and Kern : Peridermium 



cognized forms of aecia appear to belong to Melampsorella, 

 although only one species of that genus has yet been found within 

 our limits, which may be due to their being inconspicuous. In 

 the remaining lines of the table the discrepancy between aecia 

 and telia is only what would naturally occur by this method of 

 tabulation, and one which may confidently be expected to be re- 

 moved when more collections are made and studied. 



To ascertain the particular species represented by the numbers 

 in this table reference may be made to the following pages for 

 those of Peridermium. The species of Coleosporiiim are embraced 

 in a paper presented before the Botanical Society of America one 

 year ago by one of the present writers, but not yet published. 

 The species of this latter genus and of the other telial genera will 

 soon be described in the current North American Flora , including 

 a few species that are new. 



Thanks are due, and are hereby most heartily accorded, to the 

 curators of many important herbaria for the privilege of examining 

 and studying the collections of Peridermium, and to many indi- 

 vidual botanists, who have assisted with specimens and various 

 information. The following herbaria proved especially helpful : 

 New York Botanical Garden, New York State Museum, Missouri 

 Botanical Garden, Cryptogamic Herbarium of Harvard University, 

 ■Cryptogamic Herbarium United States Department of Agriculture, 

 Holway Collection in University of Minnesota, Cornell University, 

 Iowa State College, Mississippi Valley Laboratory at St. Louis. 

 We are particularly indebted to Messrs. W. G. Farlow, W. A. 

 Kellerman, H. Klebahn, P. L. Ricker, P. H. Rolfs, H. von 

 Schrenk, C. L. Shear, C. H. Peck, S. M. Tracy, L. M. Underwood 

 and H. H. Whetzel. The ready cooperation by all botanists to 

 whom our special problems were presented, has enabled us to 

 give a fairly complete account of present available knowledge re- 

 garding American forms of Peridermium. 



~ . , Analytical key 



rycnia subcorticular. 



Peridium one cell thick. 



Peridia very low and fragile. 



Spores thin-walled, without smooth spot. I. P. delicaiulum 



Peridia medium high (0.5-0.8 mm.). 



Spores thin -walled, without smooth spot. 2. P. montanum. 



