140 Plant Tissue Culture 



on the table in front of the operator. The plug is 

 removed from the first, and a sound, rapidly grow- 

 ing root tip is selected and picked up on a long 

 chromel-wire loop. Usually two loops are em- 

 ployed alternately so that one is always in the 

 sterilizing beaker while the other one is in use. 

 The stock flask is plugged and set on the table, the 

 uninoculated flask is taken up in the left hand, its 

 plug removed with the right hand which still holds 

 the transfer loop, and the culture fragment is in- 

 serted, the flask plugged and returned to its tray. 

 The loop is returned to the boiling water and a 

 fresh one taken up. The process is then repeated 

 with another flask. In choosing tips for inocula- 

 tion, it will be noted that occasionally a root which 

 does not visibly differ from the others will never- 

 theless sink to the bottom of the flask instead of 

 floating at the surface. Such tips should not be 

 used, as experience has shown that they are regu- 

 larly retarded in their development. Such re- 

 tarded tips will sometimes recover completely, but 

 they cannot be relied on to do so. What the cause 

 of this condition is is not known, although it ap- 

 pears to be some obscure characteristic of the 

 general "state of health" of the stock culture 

 before excision. 



The above description applies to the setting up 

 of root cultures. The procedure for callus cul- 



