146 Plant Tissue Culture 



without apparent injury and, while growing very 

 slowly at such temperatures, will resume a normal 

 growth rate within a few days when removed to 

 higher temperatures (White, 1937, 266). Aside 

 from these two requirements, of maintained tem- 

 perature level and protection from direct insola- 

 tion, together with protection from traces of gases 

 or volatile materials, the environmental require- 

 ments of plant tissue cultures are not especially 

 exacting. 



Flask cultures of the type described above have 

 great flexibility and permit considerable freedom 

 of manipulation. They can be handled easily and 

 do not readily become contaminated. They do, 

 however, occupy a good deal of space, the nutrient 

 evaporates rapidly with consequent alteration in 

 its solute concentration so that the cultures must be 

 transferred at frequent intervals, and they require 

 large volumes of nutrient. Conditions may some- 

 times arise under which these objectionable fac- 

 tors outweigh the difficulties of manipulation in 

 small space so that it is desirable to grow cultures 

 in test tubes, either on agar or in liquid nutrient. 

 The size of the tube to be used will depend on the 

 requirements of the particular experiment. Gey 

 uses a special 15 X 100 mm. tube for " roller tube" 

 cultivation of animal tissue cultures (Gey, 1933, 

 129; Gey and Gey, 1936, 130). This method has 



