Culture Techniques 147 



not been tried with plant tissue cultures but de- 

 serves attention. Lewis uses ordinary 15 X 150 

 mm. test tubes for the same purpose (Lewis, 1935, 

 419). Callus cultures have sometimes been grown 

 in 2 ml. of nutrient in 12 X 100 mm. serum tubes, 

 but such cultures must, of course, be removed from 

 the tubes for any kind of manipulation, even for 

 division in order to make transfers. Tubes 25 

 X 150 mm. without lip and charged with 10 ml. 

 of nutrient, have proved to be a fairly satisfactory 

 compromise between the advantages and disad- 

 vantages of the test tube and the Erlenmeyer flask. 

 They are shallow enough and have wide enough 

 mouths that considerable dissection and other 

 manipulation can be practiced on the cultures 

 without removing them from the tube. The liquid 

 surface is still small enough in proportion to the 

 volume to reduce evaporation to a considerable 

 extent, yet the depth of liquid is small enough to 

 permit some degree of aeration without special 

 precautions. Such tubes are especially well 

 adapted for routine callus cultures on agar. Eoot 

 cultures in tubes must be watched to see that the 

 tips do not turn upward when the culture reaches 

 a length greater than the diameter of the tube. 

 Otherwise, with continued growth the tip may be 

 forced out into the air where it will no longer grow 

 satisfactorily. 





