E. H. NEWCOMB 423 



mum size in 12 to 15 days. Its morphology and development have been 

 described by Rosen (19). 



The walls and floor of the mature gall are many times thicker than the 

 normal lamina, and the mesophyll consists of a disorganized mass of 

 much enlarged, irregularly shaped cells. There are few stomata, and an 

 almost complete lack of air spaces. The paucity of chloroplasts is 

 especially noteworthy and becomes more pronounced as the galls age. 

 Although the galls usually occur on leaf veins, their vascularization is 

 poor due to the marked hyperplasia and the failure of small veins to 

 develop. The expressed saps of both young and old gall and normal leaf 

 tissues have pH values of from 3.0 to 3.2. 



The young galls selected for study, about 2 mm. in diameter, were on 

 young leaves 2-3 cm. long. They were compared both with normal con- 

 tiguous tissue and with that of normal leaves of approximately the same 

 age and size. In the study of mature tissues, gall activity was compared 

 with that of contiguous normal tissue, and leaves of approximately the 

 same size and position on the branches were used. The results in Tables 

 I and 2 represent averages of several experiments. 



The respiration of young and old phylloxera galls is compared with 

 that of normal leaf tissue in Table i. It is noteworthy that both young 

 and old galls have a markedly lower percentage dry weight than the 

 normal tissue. Furthermore, as the galls mature they decrease still 

 further in percentage dry weight, although the normal tissue increases 

 slightly. Consequently, the respiratory rates of gall tissues are higher 

 than those of normal tissues on a dry weight basis, although lower on a 

 fresh weight basis. 



The respiratory quotients are close to unity, indicating respiration at 

 the expense of carbohydrate. Both normal and gall cells ferment under 

 nitrogen, the ratio of fermentative to respiratory carbon dioxide being 

 0.84:1 and 0.66:1 for young leaves and galls, and 0.68:1 and 0.85:1 for 

 old leaves and galls, respectively, on a dry weight basis. While intact 

 young galls in air show the same R.Q. as the sUces, old galls, due to thick- 

 ness and the impervious epidermis, show a high R.Q. indicating that 

 oxygen is limiting the respiration, and that some fermentation is oc- 

 curring (Table i). On slicing such galls, it is found that the oxygen 

 consumption rises and the R.Q. drops to unity. 



Homogenates of gall and normal tissue were assayed for oxidase ac- 

 tivity. Cytochrome oxidase activity could not be demonstrated in the 



