THE USE OF THE MANUAL 85 



pression or complete disappearance, loses the arbitrary diagnostic character 

 which furnishes the basis for separating two adjacent groups. In such cases 

 it has at times seemed more practical to add such a species to the group most 

 nearly allied to it by general colony aspect, but to cross-reference it to the 

 related group. 



The detection and description of species hitherto unrecognized neces- 

 sitates extensive review of the literature and restudy of available living 

 cultures of at least one whole section of the great genus Aspergillus. Unless 

 the one who encounters a form that he cannot recognize under names 

 already in the literature is prepared to investigate his form adequately in 

 relation to the whole genus, he should not describe his organism as a new 

 species. 



Summarized 



Comparative study of the taxonomic literature brings out the need for a 

 standardized series of morphological and descriptive terms into which the 

 many usages introduced in the two centuries since Micheli can be translated. 

 Variations in measurement are deemed significant only if they exceed the 

 common limits between closely related organisms and predominate in the 

 preparations examined. Ranges in measurements are more significant 

 than exact dimensions of either selected structures or averaged values based 

 upon many measurements. 



Merely quantitative variations are not recognized as warranting separa- 

 tion of species. For example, differences in the shade of color, or the in- 

 tensity of a particular reaction, especially when other strains are found 

 to fall between the "old" and proposed "new" species, are not regarded as 

 species characters. Such proposed names either fall to varietal status or to 

 synonymy. 



The names not accepted here fall into several categories. (1) Many are 

 listed as synonyms because they are believed to have been given to variants 

 not recognizable by dependable and interpretable differences from other 

 members of the same series. (2) Fantastic variants, or "monsters", 

 appearing in culture may, like "Cladosarum", be maintained in the labora- 

 tory, but unless found perpetuating themselves in nature, clearly fall in the 

 class of "natures experiments" which do not contribute to the permanent 

 flora. Such names are not regarded as established. (3) Unidentifiable 

 species — names appearing in the literature based upon structures or re- 

 actions regarded by the describer as unique, but whose identity is so com- 

 pletely lost in large collections among series of closely related strains as to 

 make them unidentifiable by description — are listed in the check list with- 

 out characterization. 



