144 A MANUAL OF THE ASPERGILLI 



It is clear that wide mycelial or colony variations may be found in nature 

 between strains that retain the ascospore characters of the species. Several 

 such groups have been held by the authors for 30 years or more and fur- 

 nish convincing evidence that Mangin was justified in using the ascospore 

 as the stable and readily determinable integrating character. Some of these 

 forms retain colony characters in fairly stable form through many transfers 

 on many laboratory substrata and over a period of years. Others grown in 

 various substrata in Petri-dish cultures show sectors or other irregularities 

 in colony habit, which can be picked out and established as strain variants 

 that maintain their special characteristics in continuous culture. 



The possibility that variants of similar nature might be induced by chemi- 

 cal stimulation led Thorn and Steinberg (1939) to select from the authors' 

 collection certain strains that had remained fairly constant for many years. 

 Of this group they subjected strain NRRL No. 90 of A. amstelodami, found 

 apparently stable for 30 years, to extensive chemical stimulation (1940a). 

 These experiments yielded two groups of effects: (1) A progressive reduc- 

 tion in the production of conidial heads and of perithecia, and (2) a great 

 increase in the mass of vegetative mycelia. In no case was spore produc- 

 tion completely suppressed although reduced to inconspicuous quantity. 

 The conidia and ascopsores when examined were found to have retained 

 the size and markings characteristic for the species, whereas the mass of 

 vegetative mycelium became excessive and formed a floccose or cottony 

 mass entirely different in colony appearance from the original. 



At this point they reversed the procedure and applied stimulants designed 

 to reestablish spore production (1940b). As a result, the final cultures 

 show abundant green heads with normal conidia and numerous perithecia 

 with ascospores retaining the characters of the species. In routine labora- 

 tory examination these extreme variants would not suggest the original 

 strain of A . amstelodami, although both types of variants produce conidia 

 and ascospores typical of the species. 



In 1928, Barnes studied the possibility of heat in inducing variations. 

 He used a strain reported as "Eurotium herbariorum (Wigg) Link," which 

 had been isolated and maintained in his laboratory for several years without 

 apparent changes. Unfortunately, no description of his normal strain was 

 given, but a strain received from Westerdijk as "Barnes' normal strain" 

 proves to be identical with A. amstelodami (Baarn strain, NRRL No. 89; 

 or strain No. 90 as used by Thorn and Steinberg). No reasons were offered 

 for the original identification. 



Barnes described a series of experiments in which the spores of his or- 

 ganism were subjected to heat under varied conditions, then planted. 

 From the resulting colonies he described 11 variants, 6 of which are avail- 

 able in the Centraalbureau. The authors' transfers of these have been 



