222 PRINCIPLES OF SOIL MICROBIOLOGY 



The KC1 may be replaced by CaCl 2 and the reaction adjusted to 

 pH 7.3. 25 Organic media may also be employed. Various proteins, 

 including peptone, can be used as sources of nitrogen; sugars (glucose, 

 fructose), higher alcohols (mannite, glycerol), and organic acids (in 

 the form of neutral salts) can be used as sources of carbon. Various 

 decoctions of hay, manure, peas and soil extracts can also be used, 

 especially when the N and P content of the latter is increased by the 

 addition of inorganic salts. Of the various organic media suggested, 

 mention may be made here of two : 26 



(a) Cane sugar 10 grams (b) Malt extract 890 grams 



Asparagine 2 grams Glucose 29 grams 



Peptone 8 grams Peptone 0.5 gram 



Gelatin 80 grams Asparagine 0.5 gram 



Water 900 cc. Gelatin 80 grams 



To obtain inorganic solid media, add 15 to 20 grams of washed agar 

 to one of the above solutions. In addition, soil, peat, sand and 

 gypsum blocks can be used very readily, the last two moistened with a 

 nutrient solution. To eliminate all traces of organic matter silica gel 

 can be employed. 



Distribution of algae in the soil. The soil is a favorable medium 

 for the growth of algae, which require only a relatively small amount 

 of moisture to replace that lost by the protoplast in drying. 27 In view 

 of the fact that algae can develop on organic media also in the dark, 

 their existence in the soil even below the sufacee is made possible. 



The occurrence of algae in the soil, particularly that of diatoms, 

 has been referred to by a number of earlier writers. 28,29 Esmarch 30 

 attempted to determine the distribution of algae on the surface of the 

 soil, their presence in the subsurface, and whether cultivation influenced 

 their distribution. Four types of uncultivated soils were used : sandy 



24 Fred and Peterson, 1925 (p. 378). 



26 Beijerinck, M. W. Over gelatine culturen van eencellige groenwieren. 

 Verh. Prov. Utrechtsch. Genootsch. Kunst en Wetensch. 1S89, 35-52. (Centrbl. 

 Eakt. 8: 460-462. 1890.) 



27 Fritsch, F. E., and Haines, F. M. The moisture relations of terrestrial algae. 

 Ann. Bot. 148: 683-728. 1923. 



28 Ehrenberg, 1837 (p. 92). 



29 Gregory, W. On the presence of Diatomaceae, Philolithoria, and sponge 

 spicules in soils which support vegetation. Amer. Jour. Sci. Arts, II, 21: 434- 

 437. 1856. 



80 Esmarch, 1914 fp. 218); see also Esmarch, F. Beitrag zur Cyanophyceen- 

 flora unserer Kolonien. Hamburg, wiss. Anst. 28: 63-S2. 1910. 



