[Vol. 1 

 192 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



species which I have placed in the genus Peniophora because 

 of the presence of cystidia students may look for under Corticium 

 when, by a more hasty study of their collections, they fail to 

 detect these organs. On the other hand, students using more 

 discriminating methods than mine may detect cystidia in species 

 in which I have overlooked them, and such students will search 

 in Peniophora for species which I have placed under Corticium. 

 Species intermediate between genera always cause such trouble. 

 There are many intermediates between Peniophora and Cortic- 

 ium, yet in this particular case the advantage from the separa- 

 tion undoubtedly more than compensates for the disadvantages 

 occasioned by the intermediate species. 



The case of Peniophora has been considered at length, be- 

 cause this genus is being regarded as a precedent for subdividing 

 Stereum and grouping under Lloydella all those species which 

 have conspicuous non-sporebearing organs between the basidia. 

 Such a separation, however, would be artificial and give rise to 

 a troublesome series of intermediate species, without the com- 

 pensating advantage which accrued in the case of Peniophora 

 and Corticium. Stereum is not a genus of difficult species nor does 

 it comprise an immense number of species. It is just a fine, nat- 

 ural group of species capable of being more sharply defined 

 than it was by Fries, so as to receive some species from The- 

 lephora of Fries and to part with some to Corticium. So defined, 

 even beginners will have no trouble in recognizing species of 

 Stereum. Systematic work in mycology should strive to estab- 

 lish and maintain just such natural, clean-cut genera as Stereum. 



It seems to me best to work along constructive rather than 

 destructive lines. Fries had a wonderful ability for the per- 

 ception of the natural grouping of fungi on the basis of gross 

 morphology and habit. Since his time, research has greatly 

 enlarged the knowledge of the internal structure of fungi and of 

 the organs of propagation. The value of such organs in the 

 classification of seed plants is well known. It is feasible to 

 modify somewhat the genera of Thelephoracece as defined by 

 Fries, in accordance with the true relationships and differences 

 shown by the present knowledge of internal structure, basidia, 

 and spores, and a system results which is the natural evolution 

 of taxonomic and morphologic study of Thelephoracece. This 



