Culture Techniques 151 



have not yet been successfully manufactured. 

 Quartz covers are much too expensive for routine 

 work. Some progress has been made towards 

 solving this problem by dipping glass covers in 

 chemically and physiologically inert plastics such 

 as ethyl-methacrylate (du Pont), "Clarite," etc. 

 This method has given considerable promise, but 

 a reliable technique for obtaining duplicable re- 

 sults has not yet been perfected. At present, this 

 seems, however, to be the best lead. 



Methods. Hanging-drop cultures, of course, re- 

 quire very minute amounts of both tissues and 

 nutrients. Methods for their preparation are 

 described in great detail in Parker's (1938, 26) 

 recent handbook. The nutrients can be sterilized 

 in either small flasks or test tubes. Sterile pi- 

 pettes with sterile rubber bulbs must be provided. 

 The material to be cultured is cut up into pieces 

 of the required size — root tips 0.5 mm. or less in 

 length (Chambers, 1923, 43, 1924, 44; White, 

 1932, 89), bits of callus, intercalary meristems 

 (Scheitterer, 1931, 109), seed primordia (White, 

 1932, 89), small bud centers (White, 1933, 116), 

 etc. — and is placed in sterile nutrient in watch 

 glasses which will be set at the operator's left. 

 Instruments, covers, and slides are placed in 

 front. The slides are first prepared with a small 

 drop of vaseline on each side of the depression 



