[Vol. 5 

 178 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



iomycete, and finally referred by Fries with doubt to Cor- 

 ticium and regarded by Quelet as a Cyphella. 



Into Aleurodiscus have been assembled species of related 

 structure which were originally published in Corticium and 

 Stereum on the basis of form of fructification, but which are 

 noteworthy by basidia and spores often enormous in dimen- 

 sions for the genera to which these species were originally 

 referred, and which sometimes have paraphyses of remark- 

 able form, and the fructification greatly thickened in some 

 species by so large an amount of incrusted or granular mat- 

 ter as to render it very difficult to make out the detailed struc- 

 ture of basidia and paraphyses in good sectional prepara- 

 tions. The granular and crystalline matter may be dissolved 

 from the sections by warming them on the slide in a few drops 

 of dilute hydrochloric acid, but with the disadvantage of leav- 

 ing the paraphyses and other organs with rather vague out- 

 lines, as though somewhat collapsed or disorganized. 



Some species now referred to Aleurodiscus are intermediate 

 between this genus and other genera by the absence of any 

 notable development of some one or other of the foregoing 

 characters, and it is too largely a matter of personal opinion 

 as to just which species should be transferred. On the whole, 

 Aleurodiscus is probably useful, although bound to be a source 

 of confusion by introducing into a scheme of classification 

 based upon form and general structure of fructification a con- 

 flicting scheme of classification based upon rather trivial, and 

 often poorly shown, features of microscopic detail, with dis- 

 regard of diversity in form and general structure of fructi- 

 fication involved. Innovations of this kind should certainly 

 be exceptional. 



Of the 25 species of Aleurodiscus which have been recog- 

 nized up to the present time, 14 occur in North America, 8 

 in Europe, 5 in Asia and Australia, 2 in Africa, and 2 in 

 South America. A. acerinus is the only one of these which 

 is of world-wide distribution; A. amorpJius is the only other 

 species common to both Europe and North America, and in 

 North America it is restricted to northern United States 

 and Canada. Only 3 species, A. acerinus, A. candidus, 



