494 



SlLBERBERG ! STIMULATION OF STORAGE TISSUES 



Nevertheless, this was one factor which made the callus formation 

 irregular, although it does not fully account for the fact that in 

 most instances the callus formed in clumps, instead of making a 

 uniform covering over the entire surface of the specimen. For 

 this reason the observations on the gross appearance were thought 

 to be of greater significance than any microscopical observations 

 made on the specimens would be. In regard to the formation of 

 meristem beneath the surface, none at all was formed in many ex- 

 periments, even when callus was abundantly present Its formation 

 seemed to be dependent somewhat upon the age of the plant, and 

 was too variable to furnish a basis for any conclusion. In regard 



Figure 3. Sections of stimulated and unstimulated tissue of '*kohl-rabi," cut 

 verticallyto thesurface. Two weeks aftersettingup experiment ; a, showing the callus 

 formation as it appears pretty evenly all over the surface of the tissue, in the control ; 

 if showing the callus formation in tissue stimulated with N/i2 zinc sulphate, which is 

 more irregular in its formation. See figure 2. Magnified 38 diam. 



to the callus, observations were taken upon twelve experiments 

 using solutions of zinc sulphate from tenth to twentieth normal. 

 In six of the experiments, the specimens poisoned with twelfth- and 

 fourteenth-normal solutions formed callus more quickly than the 



