64 A MANUAL OF THE ASPERGILLI 



(2) The term variant, or variation, is used loosely and reference to it in 

 this manual is not, in all cases, entirely consistent. In general, however, it 

 is applied to subcultures, or strains, arising through gradual change from 

 well-defined strains of identifiable species. The characters of a variant, 

 then, are not generally stable but subject to continued change and further 

 variation. As used by us, the term has no taxonomic implication and can 

 be considered essentially synonymous with the term "saltant" which is so 

 commonly employed in reports on variation in the Fungi Imperfecti. 

 Variants frequently appear as colony sectors, overgrowths, or other local- 

 ized areas of changed appearance or texture. When isolated in pure cul- 

 ture, they may or may not retain their distinguishing characteristics. 



NATURAL VARIATION 



Cosmopolitan species and groups of Aspergilli show adaptability to wide 

 ranges of environmental conditions. As these molds are isolated from 

 nature, variation among the members of any species, series, or group is 

 regularly encountered. Such variations commonly differ in degree rather 

 than in basic characters, and one can distinguish a series of intergrading or 

 bridging forms. Even striking isolates are often unmistakably allied with 

 some well-defined species or group in this manner. Such different but 

 intergrading forms arising in nature can be considered as natural variants. 

 Natural variants of a similar kind can frequently be obtained in laboratory 

 culture by selective isolation and cultivation from sectors or other areas of 

 atypical growth, or by single spore isolations. Distinction must be drawn 

 between differences in appearance, morphology, and habit of growth result- 

 ing from inherent differences between strains, and alteration in colony 

 character in response to changes in the composition of the culture medium 

 or other environmental factors. Rigid comparative culture is often neces- 

 sary to distinguish between the two. For the present discussion, we are 

 concerned with differences that are more fundamental than direct tempo- 

 rary responses to artificial stimuli (ecads); but the latter, unless carefully 

 evaluated, may appear no less real. Rightly or wrongly, Blochwitz (1930, 

 p. 247) comments that .4. flavus, 1 in specimens collected in the Botanical 

 Garden at Buitenzorg, was called A. penicillopsis (Henn.) Rac; in the 

 Botanical Garden at Singapore, *S. vitellina Ridley; in India, S. corolligena 

 Massee; and in Columbia, .4. delacroixii Saccardo. 



Occasionally isolations are made from laboratory cultures which represent 

 sharp "breaks" from the parent strain, and since they are constant in subse- 

 quent culture, they may be considered as true mutations. Representatives 



1 The name of the original describer is only used for specimens or strains in culture 

 which were definitely attributed to the describer. A. flavus, A. niger, A. terreus, etc., 

 are series concepts as used here. 



