6 GENERA OF FUNGI 



might at first be supposed, since the immediate need is for the systematic 

 cataloguing and identifying of the immense number of forms concerned. 

 The observations and practices of the leading mycologists during more than 

 a hundred years provide the present available foundation for this and have 

 led to more or less definite usage. Through the attrition of divergent view^s 

 and by virtue of increasing information, the latter becomes in a degree objec- 

 tive and affords a correspondingly safer basis. It is imperative, however, 

 to discriminate between use and usage, and furthermore to recognize that 

 scientific usage must be continuously checked by observation and experiment 

 in order to become uniform and objective in the highest degree possible. 

 No mere lapse of time should be permitted to render current either dis- 

 crepancy or error, or to validate departures from tested and proven practice. 

 The following discussion of criteria deals with their application in the 

 present treatment, and this is based in the fullest possible degree upon the 

 practice of leading mycologists as exemplified in Saccardo's "Sylloge Fungo- 

 rum," Engler and Prantl's "NatiirHchen Pflanzenfamilien," and Raben- 

 horst's "Kryptogamen-Flora" in particular. The rule of uniformity has 

 been carried into effect in occasional instances where exceptions to an other- 

 wise universal usage have persisted to render "keying out" awkward or 

 impossible. The consideration given this matter here is not intended to 

 be exhaustive, but to be informatory and to provide a basis for future 



elaboration. 



Habit 



The actual significance of habit as a generic criterion is of course 

 unknown, but its practical value in many cases is recognized. This is espe- 

 cially true of strict parasitism and saprophytism, as it is likewise of the 

 lichen habit, involving parasitism on algae. The practice of assigning generic 

 rank to the fungicole forms is apparently valid in case of true parasites, 

 while the fimicole habit is likewise generally accepted among Pyrenomycetes 

 in particular, though not always dependable. More recently, Hoehnel has 

 insisted that the latter parasitic in other perithecia bear a distinct stamp and 

 deserve to be segregated, and his genera of this type have been tentatively 

 accepted here. Parasites on lichens have in general been accorded generic 

 value, and Saccardo, Zopf , Rehm, and Theissen and Sydow have been espe- 

 cially consistent in thus treating them. Keissler has recently objected to this 

 procedure, in spite of the current practice (1930:179), but the lichenicole 

 genera are fully as valid as the others based upon habit, and probably more 

 so than those lichen genera founded upon a difference in the genus of the 

 algal host. Much more study and information are necessary to determine 

 the exact status of the lichen-inhabiting forms. 



The general tendency has been to recognize the uredicole habit as war- 

 ranting generic segregation, and this has been extended to other distinctive 

 groups of hosts, the ferns in particular being so treated. With respect to 

 parasitism on different organs, a number of long-accepted genera are based 

 primarily if not wholly on the folicole, caulicole or floricole habit. This has 



