191 2] Morphology and Biology of Insect Galls 381 



Plate VI. 



Fig. 35- Cecidomyia triticoides Walsh on the stem of Salix cordata Muhl. 

 Transverse section showing the character of the aeriferous 

 tissue. X50. 



Fig. 36. Cecidomyia triticoides Walsh on the stem of 5. cordata Muhl. 

 Transverse section of a young gall, showing the well defined 

 nutritive layer lining the larval cavity and the protective zone 

 bounding this tissue on the outside. The aeriferous tissue is 

 also shown. X60. 



Fig. 37. Cecidomyia triticoides Walsh on the stem of S. cordata Muhl. 

 Transverse section through the nutritive and protective zones 

 of a mature gall. At the top of the figure is a dark band of 

 collapsed nutritive cells; below that a lighter coloured and 

 wider band of sclerenchymatous cells, the lumen of each filled 

 with a crystal of calcium oxalate ; and below that again a layer 

 of cambium of nearly the same width as the preceding zone. 



X150. 



Fig. 38. Cecidomyia triticoides Walsh on the stem of S. cordata Miilil. 

 Transverse section of a young gall, corresponding to the pre- 

 ceding mature form. The nutritive zone is at the top of the 

 figure, its cells are filled with rich protoplasmic contents, with 

 the exception of those in the upper row and a few scattered ones 

 throughout the zone. The protective zone is shown below this 

 tissue, but the cambium layer is not differentiated in the early 

 stages. X150. 



Fig. 39. Cecidomyia bulla Walsh on the stem of Helianthiis divaricatus L. 

 Transverse section through stem of host and attached gall, 

 showing the elongation of the fibro-vascular bundles in the 

 direction of the gall axis and the very marked proliferation in 

 the medullary rays. At the upper part of the figure, in the 

 gall cortex, an enlarged gland is partly shown and also other 

 glands at the junction of the gall and the stem of the host. X 18. 



Fig. 40. Lasioptera corni Felt, on the leaf of Corniis aUernifolia L. The 

 section shows the lower epidermis and one row of mesophyll 

 cells in normal position and also the strongly curved character 

 of the upper epidermis and the remaining mesophyll cells. 

 The normal appearance of all the cells is also apparent. X 18. 



Fig. 41. Lasioptera impatientifolia Felt, on the leaf of Impatiens biflora 

 Walt. Section at right angles to the midrib, showing the 

 generally uniform character of the cells. Cells containing the 

 mycelium of a fungus are shown a short distance in from the 



