SPECIAL METHODS 157 



Calcium Hypochlorite: . 



1. Add 10 grams of commercial chlorid of lime (titrating 

 28 per cent, chlorin) to 140 c.c. of water. 



2. Allow the mixture to settle for five or ten minutes and 

 decant the supernatant liquid. This solution should con- 

 tain about 2 per cent, of chlorin. 



3. For seed sterilization the solution may be diluted or 

 used full strength. The volume of the liquid should be 

 about five times that of the seed. 



4. Place the seed in a sterile test-tube and cover with a 

 I per cent, chlorin solution (original solution diluted one- 

 half). 



5. The time required for sterilizing varies with the dif- 

 ferent seed, about six hours for alfalfa, eight hours for 

 corn, and fifteen hours for wheat. 



Wilson, J K , Amer. Jour. Bot , vol. ii, pp 420-427, 1915. 



Silver Nitrate. — ^According to Schroeder the Gramineae 

 are not readily penetrated by silver nitrate, and withstand 

 treatment with a 5 per cent, solution for twelve to twenty- 

 four hours. In order to remove the silver nitrate wash 

 thoroughly in a sodium chlorid solution and allow the seed 

 to stand in a dilute solution of sodium chlorid for twenty- 

 four hours. 



Schroeder, H., Centbl, Bakt. (etc.), Abt. 2, Bd. 28, pp. 492-505, 1910. 



Soil Sterilization.— In order to destroy all forms of 

 microorganisms in soil a high temperature for a long 

 period of time is required. It is impossible to sterilize 

 soil by the methods commonly employed for culture-media. 

 Unfortunately, the temperature required to kill bacterial 

 spores in soil brings about other changes, chemical and 

 physical. In some cases sterilization results in. undesirable 



