VARIATION 65 



of such natural mutations which originated in the absence of any artificially 

 imposed stimuli are YuilPs A. fumigatus var. helvola (1939), A. nidulans 

 var. albus (1939), and Cladosarum olivaceum (1938). 



Intra-strain Variation 



A certain amount of variation can be expected to occur in any given strain 

 of Aspergillus. In certain species and strains this is very limited and cul- 

 tures can be re-cultivated repeatedly upon a variety of media, and at 

 different temperatures and H-ion concentrations without evidences of visi- 

 ble change other than those resulting from the immediate effects of the 

 altered environment. Many strains of Aspergillus niger are characterized 

 by such comparative stability. Other species and strains are subject to 

 continual variation with differences in character and rate of growth appear- 

 ing rather abruptly as sectors or overgrowths, or gradually developing as a 

 progressive alteration in the general aspect of the whole culture. By suc- 

 cessive and selective subculturing, strains of A. alliaceus and A. ochraceus 

 showing a marked difference in sclerotium production can be obtained. In 

 like manner, strains of A. itaconicus Kinoshita can be secured which are 

 almost completely sterile upon all media tested. The same is true of A. 

 granulosus Raper and Thorn, A. flavipes, etc. 



Working with a strain of the ascosporic species, A.fischeri, Greene (1933) 

 isolated 448 single spore cultures and among these found variant progeny 

 of two main types: (1) cultures producing very large, scattered perithecia 

 as opposed to the typical picture of many small perithecia, and (2) cultures 

 producing conidial structures in profusion, but forming few perithecia and 

 these tardily. The second type was fairly stable, whether derived from 

 single ascospores or conidia. The first type was variable, in some cases 

 reproducing the characters of the variant parent, in others reverting to the 

 character of the original stock culture. 



Hansen (1938) and Hansen and Smith (1932) have studied many of the 

 Fungi Imperfect! rather exhaustively and report that single strains of these 

 fungi are basically composed of a mycelial (M) type and a conidial (C) type. 

 By proper techniques the two forms can be separated and recombined at 

 will. While it has not been explored as yet, the possibility exists that the 

 same condition may prevail to a limited degree in the Aspergilli, and that 

 this may account for a certain amount of the intra-strain variation en- 

 countered. 



Back of variability in molds, many lines of discussion have been devel- 

 oped. Buller (1933) has frequently called attention to the unmeasured 

 possibilities of nuclear and cytoplasmic disturbance from the commonly 

 observed phenomenon of anastomosis. Vegetative hyphae belonging to the 

 same mycelium (mycelium derived from a single spore), or different mycelia, 



