68 A MANUAL OF THE PENICILLIA 



ments Co. (Difco), develop colonies usually approximating those produced 

 upon the malt agar routinely used in this Laboratory. 



Whereas malt or wort agars seldom produce colonies of Penicillia with 

 pronounced cultural characteristics, hence are of Ihnited value in diagnos- 

 tic work, they do as a rule favor the development of abundant conidia. 

 They are especially valuable in studying ascosporic species, for perithecia 

 usually develop abundantly upon these media, whereas such structures 

 may be limited or altogether lacking upon Czapek agar. Many Penicillia 

 grow more rapidly upon malt agar than upon Czapek; others do not. 

 Differential rates of growth, therefore, often provide clues to relationship 

 and identity. All of these factors entered into our decision to supplement 

 species descriptions with notes made from malt agar cultures. The prin- 

 cipal reason for this, however, rests in the wide use of such media by my- 

 cologists and stems from our belief that certain species may appear more 

 tangible if described from media with which users of the Manual are 

 possibly more familiar. 



Corn Meal Agar 



The corn meal agar as used by plant pathologists is in general repre- 

 sented by the following formula given by Shear and Stevens (1913): 



"To 40 grams of corn meal add 1 liter of water. Keep in a water bath for one 

 hour at a temperature of 58°C., never over 60°C. Filter through paper, add 1.5 per 

 cent of agar flour, steam for one and one-half hours, filter, and tube. Autoclave for 

 fifteen minutes at 115°C." 



For the present study we have prepared corn meal agar in two different 

 ways with equally good results: (A) Steep 50 gms. white corn meal (con- 

 tained in a cloth bag) in one liter of distilled water for three hours at 

 60°C.; filter and make up to original volume; add 1.5 percent agar; and 

 sterilize in the usual way. (B) The alternate procedure is to boil the corn 

 meal for one -half hour and then proceed as above. 



A stiffer corn meal agar may be made by using 100 grams of corn meal 

 and 15 grams of agar to 1000 cc. of distilled water, and heating all ingredi- 

 ents in an Arnold sterilizer for forty-five minutes or longer, if necessary, to 

 dissolve the agar. This medium is then handled without filtration and is 

 sterilized by autoclaving. 



Different laboratories using corn meal agar use quite varied quantities 

 of corn meal to the liter of distilled water, and report the final unadjusted 

 products as varying from pH 5.8 to 6.5. There appears to be in fact about 

 as many kinds of corn meal agar as there are workers who use it. 



Corn meal agar is especially useful for investigating ascosporic Penicillia. 

 In such species perithecia in limited numbers are regularly produced and 



