[Vol. 5 

 302 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



have been confused by some authors with setae and have led 

 to the publication of several such species under Hymenochaete. 

 Istvanffii has shown that there is a fundamental difference 

 between such organs and the conical, pointed setae which are 

 characteristic of Hymenochaete. In any doubtful case which 

 the student may meet it would be well to aid conclusion by the 

 color reaction with solution of potassium hydrate already 

 mentioned. In my experience the dimensions of setae are not 

 sufficiently constant to hardly more than grade these organs 

 as large, medium, and small. 



According to our present knowledge, Hymenochaete attains 

 its greatest development both in form and in number of 

 species in the western continent where it culminates in a small 

 group of indigenous stipitate species. Temperature condi- 

 tions are important in the geographical distribution of the 

 species of this genus ; this is shown by the long east and west 

 range across North America of common species, in compari- 

 son with the much shorter north and south range. Further- 

 more, Hymenochaete is a genus of tropical species rather than 

 of the cooler portion of the north temperate zone, for in con- 

 trast with the 29 species occurring from the Gulf States to 

 Brazil only 13 species are known north of the latitude of Vir- 

 ginia, and from Europe perhaps 9 species, of which 6 are well 

 known. 



Original descriptions of the species of Hymenochaete have 

 required considerable modification with regard to characters 

 referring to form, because they were based upon too limited 

 an amount of material. In the case of species of Thelepho- 

 raceae growing on prostrate logs, the inclination of the sub- 

 stratum at the point of attachment and the position of the 

 substratum as to whether over or under the fructification are 

 important in determining the habit and form of the fructifica- 

 tion. For example, a species present in quantity on a log 

 slightly raised above the ground will often show fine resu- 

 pinate specimens on the under side of the log ; about an eighth 

 of a circumference up the side of the log the upper margin 

 is reflexed, becoming longer reflexed and with a shorter resu- 



^ Physiologische Anatomic der Pilze. Jahrb. f. wiss. Bot. 29 : 410. 1896. 



