452 SOIL SCIENCE 



Potato agar: Abundant, grayish white, flat growth, usually spreading 



over the entire slope. 

 Peptone starch agar: Moderate, grayish white after 5 days, but in 



cultures from 6 to 10 days old the growth becomes a rich orange. 



The pigment diffuses through the medium very slowly. 



6. Potato cylinders: No growth in 30 days. 



7. Gelatin stab: Scant growth at surface and along track of the needle 



in 10 days. No liquefaction in 30 days. 



8. Beef broth: Not clouded in 5 days. 



9. Litmus milk: Reddened in 3 days; coagulated and digested in 25 days. 

 10. Plate cultures. 



Ammonia cellulose agar, 15 days. 



Form : Round. 



Size : 10 to 12 mm. The colonies continue to grow after 15 days, 

 and when kept in a moist chamber for 30 days the colonies 

 frequently attain a diameter of 25 mm. 



Enzymic zone: In young colonies the clearing is all within the 

 colony ; after 30 days the enzymic zone is frequently 2 to 3 mm. 



Elevation : Saucer-shaped. 



Chromogenesis : The central portion of the colony, usually 6 to 

 10 mm. in diameter, is semi-transparent grayish white. The 

 remainder is vitreous with the exception of a thin white rim. 



Internal structure: The central portion of the colony is made up 

 of loosely arranged, coarse granules. The structure of the 

 vitreous zone is indeterminate. 



Edge : Entire. 

 Peptone cellulose agar, 15 days. 



Form : Round. 



Size : 5 to 6 mm. in 15 days ; 10 to 12 mm. in 30 days. 



Enzymic zone : 2 to 3 mm. 



Elevation : Saucer-shaped. 



Chromogenesis : Central portion of colony is transparent or semi- 

 transparent grayish white. Outer portion of colony is semi- 

 transparent yellowish white. Colony is usually surrounded by 

 a thin yellowish white rim. 



Internal structure : The colony is composed of fine granules 

 loosely arranged. 



Edge : Entire. 

 Peptone starch agar, 5 days. 



Form: Surface colonies, round; imbedded and bottom colonies 

 irregularly round. 



Size: 15 to 25 mm. 



Enzymic zone : 2 to 3 mm. in 5 days ; 3.5 to 4 mm. in 10 days. 



Elevation : Flat or very slightly convex. 



Chromogenesis : Central portion of colony is a rich orange, outer 

 portion grayish to yellowish white. 



Internal structure : Consists of large granules frequently formed 

 into clumps. 



Edge : Entire to undulate. 

 Beef Agar, 5 days. 



Form : Round. 



Size : Surface colonies 1 mm. or less ; bottom colonies 3 to 4 mm. 



