124 Plant Tissue Culture 



sharply sidewise so that the stem breaks. The 

 break will take place in the region of active growth 

 where the cells possess a maximum of turgor with 

 a minimum of cell-wall deposit. Slices about 0.5 

 mm. thick are made across the stem in or near this 

 region and the pieces transferred to nutrient agar 

 or to very shallow layers of liquid nutrient. Pro- 

 liferation from very young tissues will take place 

 in all parts, while from older tissues only the re- 

 gion of the provascular strands will proliferate 

 (Fig. 17). Tubercles of white or green callus are 

 formed on the uppermost cut surface. It usually 

 requires 10 days or 2 weeks for these to attain a 

 sufficient size to justify further division. These 

 tubercles can then be separated from the underly- 

 ing non-proliferative tissue, or the culture can be 

 simply divided into a number of fragments con- 

 taining both growing and non-proliferative mate- 

 rial, and the pieces transferred to fresh nutrient. 

 Cultures from young carrot roots, potato tubers, 

 kohl-rabi, and other fleshy, only partially differ- 

 entiated members can be made in a similar fash- 

 ion. A similar technique is used in making cul- 

 tures from secondary crown-gall tumors (White 

 and Braun, 1941, 335, 1942, 336, 337). 



Miscellaneous materials. The excision of inter- 

 calary meristems such as those of grasses requires 

 much the same technique as that for the procam- 



