E. H. NEWCOMB 4^7 



of the distribution of activity of the two oxidases between such cellular 

 entities in both normal leaf and gall cells is now in progress. By centrifu- 

 gation of homogenates of normal leaf tissue, the ascorbic acid oxidase 

 activity has been found associated entirely with the fraction consisting 

 of insoluble cell debris and unfragmented chloroplasts and nuclei. No 

 ascorbic acid oxidase activity was found associated with chloroplast 

 fragments, mitochondria, or smaller particles or soluble enzymes. 



Such shifts in levels of enzyme activity may be due directly to the 

 effects of substances injected by the insect, or to environmental modifi- 

 cations resultant fiom early changes, such as the increase in tissue 

 thickness resulting in reduced oxygen tension within the tissue, poor 

 vascularization, and so on. No data have been obtained for that interest- 

 ing stage when the first cells affected by the aphid are dividing and dif- 

 ferentiating to produce a recognizable gall. The earliest stages studied 

 were of galls already possessing typical form and anatomy. 



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