136 FUNGI AS ANTAGONISTS 



Raper et al. (765) summarized the principal characters which dis- 

 tinguish the P. notatum-chrysogenum group as follows: (a) colonies, 

 at 10 to 12 days, velvety or loose-textured, plane or radially furrowed, 

 with sporing areas in blue-green shades j (b) the colonies are generally 

 characterized by abundant yellow exudate, often collecting in con- 

 spicuous droplets j (c) reverse of colony yellow, usually becoming 

 brown with agej the agar medium becomes yellow j (d) the penicillus 

 usually consists of from 2 to 5 more or less divergent columns of 

 spores; it represents an asymmetric, biverticillate structure with smooth 

 walls throughout; (e) the conidia or spores are smooth walled, vary- 

 ing from globose and sub-globose {P. notatum) to elliptical {P. chry- 

 sogenum)y and ranging in size from approximately 2.5 to 4.0 p in 

 diameter. 



Among a large number of cultures investigated, two subgroups were 

 recognized. 



Subgroup I comprises those that are characterized by penicillin yields 

 ranging from about 20 to 35 O.U./ml.; the colonies are loose tex- 

 tured, comparatively deep, heavily sporing, at first pale blue-green 

 but becoming darker with age; conidiophores often comparatively 

 long and rather coarse, bearing large penicilli; conidia typically sub- 

 globose to definitely elliptical, characteristic of P. chrysogenum. 

 These strains are common in soil and also occur in considerable abun- 

 dance in a wide variety of other natural substrates. 



Subgroup II comprises the strains that produce 50 to 80 O.U./ml. of 

 penicillin; the colonies are fairly compact or even close textured, 

 velvety throughout, dark green with abundant yellow exudate; co- 

 nidiophores bear penicilli somewhat smaller than those of Subgroup I, 

 typical of P. notatum. These strains have been isolated from soil, 

 cheese, fruits, and bread. Different isolations were found to vary 

 greatly in their capacity to produce penicillin; substrains derived 

 from these also show marked variation in productivity. 



P. notatum lends itself readily to the study of sectorial mutants. 

 These either can arise spontaneously or can be induced by special treat- 

 ments, such as irradiation with x-rays or bombardment of the culture 

 with neutrons (667). This phenomenon can be utilized for genetic 

 studies (727). Mutants have thus been obtained which produce un- 



