[Vol. 7 

 82 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



upon its publication are Stereum hirsutum, S. striatum, S. 

 purpureum, S. nitidum, and S. rugosum, no one of which was 

 designated as the type species. 



The species of Stereum are here arranged in the usual sections 

 of central-stemmed, lateral-stemmed, merismatoid, and dimid- 

 iate and effuso-renexed species; these sections are convenient 

 for locating species approximately, but one should bear in mind 

 that some species are ambiguous with regard to sectional charac- 

 ters; all the species are probably so variable that individuals 

 may be selected from most gatherings which will prove very 

 misleading for study. For example, Stereum fasciatum is 

 properly included in the section of effuso-reflexed species, yet 

 fructifications of this species do occur now and then with elonga- 

 tion of the umbo so great as to lead one to regard such a fructifi- 

 cation as lateral-stemmed. 



While Stereum is a large genus in the number of its North 

 American species, its difficulty is not proportional to the number 

 of species, for the species of each of its several sections differ 

 among themselves microscopically in the absence or presence 

 of definite recognizable organs or combinations of organs, such 

 as conducting organs containing latex (milk), vesicular organs, 

 gloeocystidia, cystidia of various kinds, and noteworthy para- 

 physes. In the determination of any species, one's effort is 

 soon concentrated upon a small group of four or five species 

 of common structure, some of which may be eliminated by 

 geographic range, spore dimensions, etc. The structural fea- 

 tures have been very important in working out the extensive 

 multiplication of species which had arisen in this genus through 

 disregard of the work of earlier mycologists. 



As heretofore noted in the case of Hymenochaete, the east and 

 west range of the species of Stereum is marked in comparison 

 with north and south range ; of our 77 species, only 7 range over 

 both north temperate and tropical areas; the other 70 may be 

 arranged in two groups, of which the 29 species comprising the 

 northern group are in the region from Canada to the Gulf states; 

 the other 41 species range from the Gulf states southward. The 

 Gulf states are a region in which northern and southern species 

 overlap in range. The excess of tropical and subtropical species 

 over northern species is due to the small number of northern 



