THE DECOMPOSITION OF CELLULOSE IN SOILS 439 



tap water. Continue the addition of the acid until the blue color disap- 

 pears ; add a slight excess of acid, shake thoroughly and allow to stand a 

 few minutes. The finely precipitated cellulose will rise to the top, due to 

 the large quantity of free hydrogen liberated in the precipitation process. 

 Shake the solution vigorously at intervals of a few minutes to dislodge 

 the hydrogen. As soon as tlie free hydrogen has escaped the cellulose 

 will settle rapidly. 



3. Wash through repeated changes of water until free from copper 

 and chlorine. After the washing is complete, bring the cellulose in the 

 solution up to 0.5 per cent, by allowing to settle a few days and siphon- 

 ing off tlie clear solution or by evaporating. Add the nutrient salts de- 

 sired together with 1 per cent of thoroughly washed agar; heat in auto- 

 clave or boil until the agar is dissolved; tube and sterilize in the usual 

 way. 



Action of the Cellulose-Dissolving Bacteria Studied on the 

 Cellulose of Plant Tissues 



While the preparation of cellulose agar from precipitated cellulose as 

 described above has proven quite satisfactory for the isolation and study 

 of organisms which dissolve typical cellulose, such as is found in filter 

 paper or in cotton fiber, it does not make possible a study of the action of 

 the organisms on the celluloses in plant tissues such as are ordinarily add- 

 ed to the soil, as stubble, roots, green manure, etc. Since the term "cellu- 

 lose" connotes a group of substances rather tlian a single chemical com- 

 pound, it seems important that methods be devised which will make pos- 

 sible a comparative study of the action of the cellulose-dissolving organ- 

 isms isolated from the soil, upon the cellulose of different plants and also 

 of the same plants at different stages of maturity. In the young plant 

 cells the walls contain almost pure cellulose, but as the plant developes the 

 cellulose originally formed is altered by the addition to it of various sec- 

 ondary products known as encrusting substances. The nature and prop- 

 erties of the resulting fiber depends, of course, upon the nature of the 

 substances deposited. 



Since many of the cellulose-dissolving organisms attack not only the 

 celluloses, but many other plant substances such as the starches, sugars, 

 and proteins, it is necessary in studying the action of these organisms on 

 the cellulose of different plant tissues, other than that of cotton fiber, to 

 separate the cellulose from the other compounds with which it is more or 

 less closely associated in the plant. It is also important that the purified 

 cellulose be separated into very fine particles such as will permit the 

 preparation of a satisfactory cellulose agar. Finely divided pure cellu- 

 lose suitable for the preparation of cellulose agar may be prepared from 

 plant substances as follows : 



