miscellaneous: tumors in absence of parasites 497 



Fig. 373.-(1), (2) and (3). Small tumors on under surface '^f ^^^li^^^^J 

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



^ ^"it^CrTss-sectiot 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 



