SiLBERBERG : STIMULATION OF STORAGE TISSUES 



497 



N/12. 



About the same as in the control — -impossible to say 



definitely whether there is more or less meristem formed. 



N/14. 



About the same as in the other two specimens. 



After twenty-one days : 



Control. — Exposed tissue dried to the edge of the meristem- 

 atic layer, and some new meristem forming inside the first layer. 



N/12. 

 N/14. 



Quite a little more meristem than in the control. 

 About the same amount as in the specimens poisoned 



with N/12 ZnSO,. 



In view of these results it seems fair to make the following 

 conclusions. Twelfth- and fourteenth-normal solutions of zinc 

 sulphate stimulate the formation of meristematic tissue in the potato. 

 A tenth-normal solution neither stimulates nor inhibits the forma- 



FiGURE 4. Section of stimulated and unstimulated tissue of potato tuber, cut verti- 

 cally to surface. Three weeks after setting up experiment; a, showing the callus 

 formation in control specimen ; b, showing callus fonnation in tissue subjected to the 



N/ 



Magnified 53 diam. 



tlon of meristem. The tissue recovers from the effects of eighth- 

 normal solution in about three or four days, from fourth-normal 

 solution in eight or ten days, from half-normal solution in about 

 seven days, and from the normal solution in from thirteen to fifteen 

 days. Owing to the method by which the solutions must neces- 

 sarily be applied, it is, of course, impossible to determine definitely 



