How Cultures Are Started 121 



darkness or in dim light until adventitious roots 

 emerge. The cuttings are removed in a sterile 

 room, the roots carefully severed and placed 

 one by one in flasks of nutrient. (Fig. 33). Using 

 this simple procedure, many roots will, of course, 

 be contaminated with molds or bacteria and 

 must be discarded. Some, however, will regu- 

 larly remain sterile. These can then be made to 

 serve as the origins for clones of sterile root cul- 

 tures each carrying the virus of the disease with 

 which the original cutting was infected. With 

 slower-rooting cuttings, greater precautions 

 against contamination will be necessary, and the 

 surfaces will have to be sterilized by some one of 

 the methods described for the sterilization of 

 seeds. Whatever sterilizing agent is used, it 

 must be removed by thorough washing with sterile 

 distilled water. The containers must also be ster- 

 ile and all manipulations must be carried out 

 aseptically. A high yield of sound aseptic root- 

 lets cannot be expected under these exacting con- 

 ditions, but they can be obtained with some 

 patience. 



Cambium. Theoretically the cambium layer, 

 since it continues to grow throughout the life of 

 the plant, for hundreds and even thousands of 

 years in some cases, should be excellent material 

 for cultivation. Practically, however, it offers of 



