62 A MANUAL OF THE PENICILLIA 



modified the method of preparation as follows (freely translated) : 



The tartaric acid crystals were shaken in lukewarm distilled water and let stand 

 until dissolved. The magnesium carbonate was then added and dissolved at once. 

 The ammonium salts were dissolved in separate vessels with the water slightly 

 warmed. The rest of the components were dissolved together in about 300 cc. of 

 water. The gelatin or agar was dissolved separately in about 500 cc. of water. After 

 the gelatin or agar was fully dissolved, the other solutions were added while the mass 

 was stirred. No precipitate formed when the mixture was properly made. No fil- 

 tration or c'e?r"ng process was needed with high grade ge'atin. The gelatin medium 

 was sterilized in steam on the first and third days. Agar media were autoclaved. 

 Layers of substratum 4 to 5 mm. deep were used in the petri dishes. 



Biourge sometimes used 0.75 percent of agar-agar and 5 percent of gela- 

 tin with this solution to prepare a solid substratum for general culture 

 work with saprophytic molds. Zaleski made his solid substratum by 

 adding 1.5 to 1.7 percent of agar-agar or 10 percent of gelatin. 



Bean Agar and Potato Agar 



Thom, in his "Cultural Studies" (1910), used potato agar and bean agar 

 with and without sugar. The method of preparation follows: 



Bean agar. The directions for making bean decoction were obtained from Maze 

 at the Pasteur Institute in Paris. Common white beans were heated in five volumes 

 of water. Boiling was stopped just before the swelling of the cotyledons ruptured 

 the seed coats. This gave a clear, slightly yellowish liquid which filtered readily, 

 yet contained sufficient nutrients to grow many species normally. Agar was added 

 as desired. Since this decoction is poor in available carbon, the addition of sugar 

 was often desirable for many species. 



Potato agar. This medium was selected because of its use in many mycological 

 laboratories. The potatoes were carefully washed, pared, and sliced, then slowly 

 heated for about two hours in approximately two volumes of water. At the close of 

 the heating the water was allowed to boil. The whole was then filtered, water being 

 added to make up the losses from evaporation and filtering. To this was added 1 per 

 cent of shredded agar. It was then heated for from twenty to thirty minutes in the 

 autoclave at 120°C. or higher, after which it was ready for use. If cloudy, it was 

 refiltered through absorbent cotton. Titration showed that the medium was nearly 

 neutral to phcnolphthalein; consequently it was used without neutralizing. Uni- 

 form composition was not claimed, but cultures of the same species grown upon suc- 

 cessive lots of this medium showed negligible differences in morphology. 



Potato-Dextrose Agar 



This medium, which is probably more widely used by plant pathologists 

 than any other, will support good to luxuriant growth of most species of 

 PenicilUnm. Colonies, however, generally fail to develop well marked 

 cultural characteristics of a type useful in separating species. It has not, 

 therefore, occupied a prominent place in the taxonomic literature of 

 Penicillium, As in the case of corn meal agar, many different methods of 



