MISCELLANEOUS: TUMORS IN ABSENCE OF PARASITES 497 



FIG. 373. (1), (2) and (3). Small tumors on under surface of cauliflower 

 leaves produced by formaldehyde (gas), exposure of February 21, 1917. Time, 

 8 and 7 days. X 5. 



(4, Cross-section, showing nature of the overgrowth. The dark green palisade 

 tissue is only slightly involved. At top, normal thickness of leaf tissue. From 

 an unstained free-hand section. 16 mm., 4 oc., bellows at 35. 



32 



