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UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



room, but makes it difficult to maintain the temperature and moisture 

 conditions regular and uniform in all parts of the bed. 



In the callusing bed we should endeavor to hasten and perfect the 

 union of stock and scion as much as possible while delaying the start- 

 ing of the buds and the emission of the roots. The latter processes 

 require more moisture than the formation of healing tissue, therefore 

 the sand should be kept comparatively dry. Between 5 and 10 per cent 

 of water in the sand is sufficient. The purer the sand the less water is 



FIG. 15. Showing the independence of root 

 and callus formation. 



necessary. There should be a little more moisture present than in the 

 sand used for keeping the cuttings over winter. Too much moisture 

 will stimulate the emission of roots and starting of buds without aiding 

 the callus formation, as is well shown in Fig. 14. 



The formation of callus, or healing tissue, is a perfectly distinct 

 process from the formation of roots. The independence of these pro- 

 cesses is shown in Fig. 15, where an abundant growth of callus is 

 shown on the cut surface, while roots are shown growing only above 

 the cut surface. 



