(425) 



Fungorum" from time to time but both that work and that of Dietel 

 in the "Natiirlichen Pflanzenfamilien" while bringing together the 

 systematic information are in nature only compilations. There 

 has therefore been a gradual accumulation of knowledge regarding 

 the genus but no complete monographic study has appeared up to 

 the present time. 



As intimated in the prefatory note, this paper attempts to pre- 

 sent a systematic treatment of all the species known to occur in 

 any part of the world so far as the writer has been able to make 

 them out from an examination of the literature and herbarium 

 specimens, supplemented by extensive field studies in the United 

 States. The present paper describes 29 species which have the 

 full life-cycle known, 4 known only in the telial phase, and 7 known 

 only in the aecial phase; a total of 40 species. 



In preparing the descriptions the author has attempted to make 

 them as brief as possible and still have them include the chief 

 diagnostic characters. If in some instances they appear rather 

 long it is because it is thought best not to sacrifice accuracy for 

 the sake of brevity. Descriptions of the pycnia have been omitted 

 under the different species because as a rule these structures do 

 not present very important diagnostic characters. Pycnia are 

 known in every species where the aecia are known (except G. 

 bermudianum), and they have been examined and sectioned 

 but since the characters are fairly uniform* it is thought that 

 the generic description will suffice for this stage. Moreover, 

 even with the fullest descriptions it would be impossible to de- 

 termine specimens having only this stage present. 



In the aecia, the form which the peridium takes on after de- 

 hiscence has been used as the chief gross character. Among the 

 microscopic characters of first importance are the nature of the 

 surfaces of the peridial cells and the relative thickness of their 

 walls. The value of the peridial cell in defining the species has 

 been pointed out by Dr. Ed. Fischer (1895), and the writer has 

 also contributed a special paper (1910 2 ) on this subject. Con- 

 cerning the surface characters of the peridial cells it may be well 

 to quote from the latter paper where the descriptive terms to be 

 used are fully explained : " With regard to the surfaces of the peridial 



* It is possible to pick out certain species which might show considerable 

 difference in the size of the pycnia, for instance in G. germinate they are 160- 

 270^ in diameter by 150-230,* high, with ostiolar filaments 90-150,. long, 

 while in G. Nidus-avis they are 120-155,. in diameter by 80-112*. high, with 



