igia] Morphology and Biology of Insect Galls 379 



Fig. 13, Chermes floccus Patch on the stem of Picea mariana (Mill.) 

 B.S.P. Transverse section, showing the smaller accessory resin 

 ducts. X25. 



Fig. 14. Pemphigus rhois Walsh on the leaf of Rhus typhina L. Longi- 

 tudinal section of a young gall, showing a number of glands. X 15. 



Plate III. 



Fig. 15. Pachypsylla celtidis-mamma Riley on the leaf of Celtis occiden- 

 talis L. Section through the larval cavity, showing the cambium 

 tissue and the sclerenchyma sheath bordering it on the outside. 



X15. 



Fig. 16. Memythrus tricinctus Harris on the stem of Populus tremuloides 

 Michx. Cross section through the thickened annual rings, show- 

 ing the clumps of bast fibres. X20. 



Fig. 17. Stagmatophora ceanothiella Cosens on the stem of Ceanothus 

 americanus L. Cross section, showing secondary growth in the 

 wood and the abnormal glands in the cortex. X50. 



Fig. 18. Normal stem of the host of the preceding species. Section 

 taken near the gall ; glands are not present in the cortex. X50. 



Fig. 19. Glands found in the cortex of S. ceanothiella Cosens; these corre- 

 spond to those shown in Fig. 17. X 150. 



Fig. 20. Gnorimoschema gallcBsolidaginis Riley on the stem of Solidago 

 canadensis L. Transverse section showing an abnormally large 

 gland in the cortex. X45. 



Plate IV. 



Fig. 21. Eii^cosma scudderiana Clemens on the stem of Solidago canadensis 

 L. Transverse section showing the proliferation in the bundles 

 and the medullary rays and also the enlarged glands in the 

 cortex. X75. 



Fig. 22. Gnorimoschema gallceasterella Kellicott on the stem of Soli- 

 dago latifolia L. A transverse section through one side of the 

 aperture of exit, the material used by the larva in smoothing 

 the sides of the hole for the reception of the plug is shown. 

 The cross checking in this material can also be seen. X 120. 



Fig. 23. Neolasioptera perfoliata Felt on the stem of Eupatorium per- 

 foliatum L. Transverse section showing an unusual type of 

 cell division in the cortex and epidermis of this gall. The glands 

 shown near the inner boundary of the cortex are not found in 

 the normal stem at the same height. X55. 



Fig. 24. Rhabdophaga strohiloides Walsh on the stem of Salix cordata 

 Muhl. Longitudinal section showing the larva in contact with 

 the small celled tissue at the apex of the stem. X25. 



