ISOLATION AND PURE-CULTURE METHODS 31 



solid substratum, serving principally, perhaps, as a means of aeration. 

 Wads of pure filter paper, or elder pith which has been carefully 

 purified, are both serviceable. 



Certain parasitic, fleshy, or bracket fungi may be grown to advan- 

 tage upon dead or normal wood. With a proper regulation of the 

 moisture content of the culture chamber fruiting is often readily 

 induced upon such media when other substrata fail. 



Silicate jelly. Silicate jelly as a substitute for gelatin and agar 

 was introduced primarily to overcome the difficulties experienced 

 in isolating certain organisms in the cultivation of which it is de- 

 sirable to avoid organic media. There is, however, a much wider 

 use for this preparation. As finer methods are developed it be- 

 comes more and more desirable to employ synthesized media for 

 a variety of purposes. At best gelatin and agar are of uncertain 

 composition, and when, for example, one wishes to determine 

 accurately the value of nutrient substances for an organism re- 

 quiring solid media, silicate jelly is most serviceable. This material 

 is not difficult to prepare when precautions are taken, and the 

 writer has found it practicable in connection with any mineral or 

 organic nutrients tested. 



The following materials and special apparatus will be required 

 for 500 cc. of the silicate jelly. 



a. i Baume hydrometer for liquids heavier than water. 



b. 200 cc. HC1 (sp. g. 1.10 Baume). 



c. 200 cc. sodium silicate (sp. g. 1.09). 



d. collodion sacks for dialyzing. 



e. 100 cc. nutrient salt solution five times desired strength. 

 Stock solutions of b and c may be kept on hand, also of e, if 



the same nutrients are to be employed in many experiments. 

 Strong hydrochloric acid is diluted with pure distilled water to 

 test 1.10 Baume at 15 C. 



Sodium silicate, water glass, is obtainable at a specific gravity 

 of about 1.38 to 1.42. Distilled water may be added to this slowly 

 until the hydrometer registers 1.09 B. It will usually require 

 about seven or eight times as much distilled water as silicate to 

 give the specific gravity desired. When required the standardized 

 silicate is then added cautiously (dropping rapidly) to the acid, con- 

 stantly stirring. 



