MISCELLANEOUS: TUMORS IN ABSENCE OF PARASITES 485 



earlier (2- to 3-day) stages of the tumor development (hyperplasias 

 on cauliflower leaves resulting from acetic acid sprays) and al- 

 ways found, judging by differences in staining, indications of 

 at least a few killed cells under the stoma through which the 

 acid penetrated (Fig. 378). 



In 1918, Harvey, of the U. 8. Department of Agriculture, 

 showed that cabbage leaves, exposed to -3C., freeze at first 



FIG. 363. Cabbage pith showing a hard woody cylinder which developed 

 after injecting a solution of sodium bicarbonate. Needle track at N. Under 

 AT a little of the normal wood cylinder. 



irregularly in small spots and if the freezing be interrupted at 

 the right moment, say at the end of 1 2 hour, and the plants re- 

 turned to proper conditions, overgrowths (Fig. 379), which 

 judging from his sections, may be either hypertrophies or hyper- 

 plasias, develop from such chilled or frozen spots (Fig. 380) 

 These frozen spots are visible at once because there is extrusion 



xylem medullary rays. The white islands in the upper part of the figure are groups 

 of hard bast fibers in cross-section. Photographed by the writer from one of Miss 

 Rumbold's slides. 



