Nebraska Forest I'uin/i. II 81 



old and already well worked, there is an abundance of material 

 still available for investigation, and I feel that the. really "start- 

 ling disclosures" are still in the future. We have so far but a 

 few very slender threads that serve merely as hints of the nature 

 of the well-woven fabric that must yet be many years in the 

 weaving. 



A complete list of the fungi found growing upon the leaves 

 of our forest trees and other woody plants would cover a number 

 of pages. Many of these are parasitic, many saprophytic, and 

 some are probably on the border line between these two great 

 types of nutrition. In some of the genera of Fungi Imperfecti 

 that are so common as "spot fungi" there are many species of very 

 doubtful validity. It is frequently quite impossible to identify 

 such species by published descriptions, and it would seem at times 

 that species had been made for such fungi upon the slightly 

 varying characters that might well be produced by very slightly 

 different host-physiology; characters that are very fleeting and 

 unstable. Over and over again in working with such forms I 

 have been puzzled because the spores were a little too long, or 

 the constrictions at the septse not deep enough, or the spots not 

 of the right color to "fit" the type description. Those who have 

 worked in Ccrcospora or Scptoria appreciate this nature on the 

 part of many fungi. And the peculiarity becomes more con- 

 spicuous the more one studies. 



I have not attempted to prepare a complete monograph of 

 the leaf fungi of Nebraska forest trees in the following pages, 

 but have merely indicated a number of the most common forms 

 from the various groups. Much more detailed work must be done 

 before a comprehensive treatment of the question can be forth- 

 coming. 



ASCOMYCETES. 



Pliacidiaccac: 



In this family (usually classified with the Discomycctcs) 

 the apothecia develop with a surrounding stroma which is usually 

 coherent with the substratum. In the beginning the apothecia 

 are closed and sunken. Later they become disk-like or elongate,, 

 single or grouped, and more or less erumpent, and finally they 

 acquire a tough and leathery, or even carbonous texture. They 

 open by a circular or transverse split and the edges become 

 turned back as more or less irregular lobes. Some species in 

 the family develop copious conidia over the stroma preceding 

 the formation of the apothecia. The most conspicuous member 

 of the family that occurs in Nebraska is the "Tar Spot" of the 

 Maple. 



