102 Plant Tissue Culture 



1939, 78, 333 ; Fiedler, 1936, 45 ; Gautheret, 1935, 

 15, 1937, 68). It is, of course, desirable to keep the 

 medium as nearly as possible of the same chemical 

 constitution as are the liquid media. Two com- 

 mon coagulants are available. Gelatin has been 

 used by some workers. This requires a concen- 

 tration of 10-20 per cent to maintain a satisfac- 

 tory consistency, which introduces not only a con- 

 siderable risk of chemical contamination but also 

 a marked adsorption factor. Agar, on the other 

 hand, will give satisfactory consistency at 0.75 

 per cent. Commercial agar is seldom free of 

 soluble contaminants and must be thoroughly 

 leached. Take 60 g. of finely shredded agar (the 

 powdered forms are likely to contain a contami- 

 nating "filler"), add 2 to 3 liters of distilled water, 

 and set aside in a cool room. Change the water 3 

 times daily for a week. After thorough leaching, 

 make up to the required volume with nutrient 

 solution, melt, filter through cotton, and distribute 

 to flasks or test tubes. These can then be auto- 

 claved and set aside to cool. 



The preparation of nutrients. While there is 

 already a considerable number of nutrients in use 

 having slightly different constitutions, the pro- 

 cedures used in their preparation will scarcely 

 vary greatly in any important details. A stock 

 example can, therefore, be given which can be con- 



