Nutrients 107 



Each tray holds forty 125 ml. Erlenmeyer flasks 

 and three trays (120 flasks) can be sterilized at 

 once in a 20-inch autoclave. They can then be con- 

 veniently handled and stored without removing 

 from the trays. While autoclaving is satisfac- 

 tory for most nutrients likely to be used in plant 

 tissue culture work, those containing dextrose are 

 somewhat thermolabile and are better sterilized 

 either in the Arnold type of sterilizer or by filtra- 

 tion through Seitz filters or Berkefeld candles. 

 These methods are all so thoroughly standardized 

 in general microbiological practice that they need 

 not be described here. 



Storage. Once sterilized, the stock nutrients 

 will keep indefinitely aside from the gradual con- 

 centration which results from evaporation. Be- 

 cause of this last factor, it is best not to use nutri- 

 ents that are more than a month old unless they 

 have been stored in a moist room. 



Special nutrients. The details presented above 

 apply specifically to the standard nutrient used 

 for the maintenance of all stock cultures in this 

 laboratory. This standard nutrient is employed 

 in most nutrition experiments as a basis of com- 

 parison designated as the control. Experiments 

 involving the stimulatory or depressant effects of 

 increased concentrations of standard ingredients 

 or of materials not present in this nutrient can be 

 set up merely by adding the required materials 



