THE USE OF THE MANUAL 83 



Species 



The species concept in Aspergillus is very difficult to define in tangible 

 terras. In this manual, the species names already in use have been pre- 

 served wherever possible. The actual material originally described under 

 a particular species name (i.e., type material) exists for but a few species. 

 If such material exists, it is more important as fixing one point, one individ- 

 ual strain in a series of intimately related variants, than tying the name 

 to extremely definite morphology. If such material is not known, compari- 

 son of large numbers of strains in pure culture with authoritative descriptive 

 information, supplemented by laboratory usages coming down from the 

 original describer, usually fixes the series or form intended. 



From such composite sources it is commonly possible to establish a fairly 

 concrete morphological aspect based upon ranges of color, differences in 

 structure, and variations in spore measurement which are repeated in great 

 numbers of isolates. In such series of isolates, there are no sharp lines of 

 demarcation when large numbers of strains are brought together. Within 

 our concept, a single strain may show much of this variability within its 

 colonies in culture, or it may reduce or suppress certain characteristics and 

 intensify others. Such variants have often been given species rank by 

 workers unaware of the existence of other variants completely bridging 

 the gap between such forms and other members of the series. Great dif- 

 ferences in biochemical activity may be shown by different strains with or 

 without contrasting morphology. Nomenclature based upon an assumed 

 correlation of a particular cultural aspect with industrial significance has 

 been offered but has proved utterly unreliable in identifying an organism 

 if lost, or in seeking a new strain to serve the same purpose. 



Two contrasting tendencies in classification are always encountered. 

 In the Aspergilli these may be represented by Mosseray (1934a) who found 

 diagnostic marks to distinguish 35 species among 63 cultures of black 

 Aspergilli in the collection of Biourge at Louvain. He later received many 

 more variants and faced the question whether to try to describe them all or 

 abandon the field. He admitted inability to write descriptions explicit 

 enough to identify them all. In contrast, Neill (1939), disregarding asco- 

 spore measurements and markings, "lumped" all of the A. glaucus group 

 into A. glaucus Link. Likewise, all of the black Aspergilli were considered 

 as A. niger van Tieghem. Forms that he did not happen to recognize as 

 belonging to one of his groups were discarded. These are extremes. 



With abundant living material before him, the student of the Aspergilli 

 can usually recognize as representative a reasonable number of forms which 

 can be described in tangible specific terms. Commonly, forms which actu- 

 ally play a significant role in nature or in biochemical processes can be 

 selected as the points around which such species descriptions are drawn. 



