miscellaneous: stimuli underlying tumor-formation 523 



Fig. 393. — Top and bottom (right side) of a pared block of sterile raw potato 

 sealed into a test tube on wet cotton February 18, 1919, and kept in dull light at 

 room temperatures (22° to 25°C.). The photos show top snd side views of the 

 two tumors, both of which have ruptured the cork layer that covered them. At 

 A', shoots are pushing. The lower left, block freshh' pared to show the thickness 

 of the cork -layer. Photographed March 22. X 5. 



