422 PLANT GROWTH SUBSTANCES 



Nierenstein proved that Cynipid larvae secrete diastase, invertase and 

 tannase, and postulated that the gallotannin of oak galls precipitates 

 the first two enzymes while the tannase hydrolyzes tannin to gallic 

 acid. Pyrogallol was presumed to arise from gallic acid by decarboxyla- 

 tion, and to be oxidized to purpurogallin by enzymes secreted by the 

 larvae, the purpurogallin then being deposited in the gall as the glycoside. 

 Although it is highly improbable that the purpurogallin, distributed 

 throughout the gall or frequently in the superficial layers of the rind, 

 arises through the action of enzymes secreted by the localized parasite, 

 its widespread occurrence in and confinement to galls and its close 

 relationship to gallotannin emphasizes the metabolic derangement in 

 galls resulting in the elaboration of polyphenolic compounds. In con- 

 firmation of Nierenstein and Swanton's generalization as to the nature 

 of gall pigments, the writer has isolated the purpurogallin glycoside, 

 dryophantin, from galls produced by two species of Cynipids not ex- 

 amined by these authors, the acorn plum gall on black oak caused by 

 Amphibolips primus and the leaf gall on white oak produced by Xysto- 

 teras poculmn. 



The respiration of two insect galls, the large oak apple produced by 

 Amphibolips cotiflitens on leaves of red oak {Quercus borealis var. maxima), 

 and the grape phylloxera gall produced by Phylloxera vitifoliae on Vitis 

 vidpina, has been compared with that of the normal leaf tissue. 



On a dry weight basis the rate of respiration of oak apple rind tissue 

 ranges from about three-fourths to one-half of that of normal oak leaf 

 tissue. The respiratory quotients of gall and normal tissues are close to 

 unity. In both young gall and leaf disks, the respiration is reversibly 

 inhibited up to about 50 per cent by such heavy-metal poisons as 

 cyanide and azide, but as both galls and leaves age, the respiratory rates 

 decline and the respiration becomes insensitive to, or rather, is even 

 slightly stimulated by these poisons. The gall respiration becomes in- 

 sensitive to the poisons earlier than the normal. The galls die in early 

 June. 



The grape phylloxera galls are initiated by young aphids on embryonic 

 bud leaves. Within 24 hours a depression is produced with hairs at the 

 periphery on the upper surface, and within 3 to 4 days the tissue below 

 and around the aphid has proliferated greatly, producing a pouch pro- 

 jecting below the lower leaf surface and opening onto the upper surface 

 through an orifice surrounded by trichomes. The gall reaches its maxi- 



