1912] Morphology and Biology of Insect Galls 353 



Solenozopheria vaccinii Ashmead. 

 „ f Vaccinium pennsylvanicum Lsim. 

 I Vaccinium canadense Kalm. 



A polythalamous gall originating from the lower part of the stem of 

 the host plant. 



In the majority of cases this gall is reniform in shape but rarely it 

 is irregularly spherical. The surface is depressed where it is attached 

 to the stem, which is almost invariably bent at that point. The colour is 

 green, often with red tints turning to brown as the gall becomes older. 



Dimensions: — Longer diameter 10-30 mm. 



At an early stage, while the tissues are still soft, the anatomical 

 structure of this gall presents practically no differentiation. It consists 

 of a mass of dense tissue, the cells of which are small and placed very 

 close together. The small-celled epidermis is covered with an exceed- 

 ingly heavy cuticle. At regular intervals small papillae occur on the 

 epidermis which seem to secrete a glandular material from small open- 

 ings at their tips. 



When the gall is mature all the cells, except a few layers below the 

 epidermis, have sclerified walls. The thickenings are decidedly heavier 

 on one wall than on the opposite. 



Aulacidea nabali Brodie. 

 Tj ( Prenanthes alba L. 



XPrenanthes altissima L. 



A polythalamous gall originating from the stem or the main root of 

 the host plant. It occurs at or near the base of the stem, usually just 

 below the surface of the ground but in some cases it is situated some 

 distance above the ground. 



The single galls are irregularly spherical, but these are generally 

 clustered in such a way as to form roughly cylindrical masses. In some 

 cases these completely surround the stem, but in others they only partly 

 encircle it. 



Dimensions: — Diameter of single gall 5-10 mm. 



The cambium of the stem stimulated to unusual activity produces 

 the abnormal tissues in this case (Fig. 66). Along the line of contact of 

 the gall with the normal stem, the cambium produces wood and bast, 

 but in abnormally large amounts, as can be seen in Fig. 66. In the gall 

 tissue proper, in place of wood, radial lines of nucleated thin-walled cells 

 occur. A few rows of vessels are interspersed among these cells. The 

 stimulated cambium produces these parenchyma cells also on the side 

 where the bast would normally occur. In the gall tissue on the outside 

 of the line of the cambium, small patches of vessels are found. These 

 have arisen from clumps of cells detached from the original cambium. 



