84 A MANUAL OF THE ASPERGILLI 



On the other hand, forms such as A.janus, A. itaconicus, A. lutescens, etc., 

 while probably rare in nature, possess sufficiently distinctive morphology 

 to warrant species recognition irrespective of other considerations. 



Varieties 



The taxonomic term, variety, is used here to designate any homogeneous 

 member of a species complex which carries most of the diagnostic characters 

 of the species but maintains one or more clearly defined differences in 

 particular characters. For example, variety alba is used for certain strains 

 of particular species in which the characteristic color of that species is 

 absent. 



There is little agreement in the literature in the application of the term, 

 variety; certain authors use the term to indicate their belief that one form 

 with particular morphological characters had its origin from another. 

 In such cases, the belief is hypothetical, not a matter of observation. 

 Sometimes previously known species were merely moved to varietal stand- 

 ing without specifying the characters upon which the decision was based. 

 Such changes are reduced to synonymy or, if entirely unsupported, are 

 occasionally ignored in this manual. The term variety is only useful if 

 definitely associated with a clearly defined variation in structures within an 

 otherwise homogeneous series of strains. 



Mutations, or Mutants 



The term mutation, or mutant, is only recognized here for forms resulting 

 from a sharp break in morphology (including color) from known structures 

 characteristic of a species, to a definitely altered and inherited contrasting 

 structure. Obviously the only excuse for the term in taxonomic usage is to 

 designate the origin of the form studied. If the source of such a variant 

 were unknown, the taxonomist would designate the form present as a 

 variety or species, depending upon the nature and importance of the changes 

 encountered. The increasing number of studies in experimental evolution 

 make recognition of induced variation taxonomically necessary. 



New Species 



The discriminating collector will occasionally find an organism markedly 

 divergent in characters from any described form. Usually these diver- 

 gences leave the organism readily recognized as a member of one of the great 

 groups. If the differences in aspect and detail of structure separate such 

 a form from the other described members of the group, and if the form is 

 found often enough to prove that it has a place in nature, description as a 

 new species is warranted. Similarly, an occasional form, either by sup- 



