Culture Techniques 139 



horizontal exposure of the opening, and the cotton 

 plug is removed with the little finger and heel of 

 the right hand and retained. The operating scis- 

 sors or scalpel is taken out of the boiling water 

 with the right hand, and all satisfactory appearing 

 root tips or callus fragments on the stock culture 

 are severed and a mental note made of their num- 

 ber. The plug is replaced, the scissors returned 

 to the boiling water, and the flask returned to the 

 tray. Root pieces longer than 15 mm. become dif- 

 ficult to pick up. Pieces shorter than 10 mm. are 

 likely to suffer considerable shock from excision 

 and to respond poorly after transfer. While 

 fragments as small as 0.1 mm. in length have been 

 grown successfully (White, 1932, 89), experience 

 has shown that those from 10 to 15 mm. long offer 

 the most satisfactory balance between these vari- 

 ous characteristics. The process of excision is 

 repeated until all available tips have been severed. 

 Since a mental note has been made of the total 

 number of root tips severed and the number re- 

 quired for the experiment planned is known, it is 

 then possible to judge how drastically the avail- 

 able pieces can be culled and still leave a sufficient 

 number. 



After all tips have been severed, the actual in- 

 oculation can be begun. A stock flask is grasped 

 in the left hand and an uninoculated one is placed 



