314 Transactions of the Canadian Institute [vol. ix 



daginis Riley, the bundles and the medullary rays are extended into the 

 gall cavity and furnish the principal part of the tissue proliferation. 

 Only a very shallow seam of normal wood is found in the galls produced 

 on S. ccesia var. axillaris Gray. 



Glands do not occur in the normal stems of either of the host plants 

 and were not found in the tissues of this gall. 



A section through the aperture of exit of a gall on S. ccesia var. 

 axillaris Gray showed that the edges of the opening had been prepared 

 by the larva for the reception of the "plug" that closed the opening. 

 The sides of this aperture, roughened by the gnawing away of the tissue, 

 would not admit of the "plug" fitting tightly and at the same time 

 slipping out easily when occasion required. Consequently the gnawed 

 surface is smoothed over by a layer of material that presents a perfectly 

 even surface. This levelling-up material is uniform in character and 

 does not show any trace of vegetable debris. At right angles to its 

 free surface, an effect resembling checking takes place, a change that it 

 has probably undergone in drying. This is illustrated in Fig. 22. 



The "plugs" of the galls produced by the genus Gnorimoschema 

 have been reported as consisting of silk and material gnawn out by the 

 larvae in preparing the openings. My observations incline me to the 

 belief that the material, forming the plug and lining the opening, con- 

 sists entirely of an exudation from the larva. It seems to be a plastic 

 silk-like substance. 



Stagmatophora ceanothiella Cosens. 



"These abnormal growths are found commonly on a main stem, but 

 rarely on a branch. The flower cluster is sometimes entirely aborted, 

 but usually only partly so, the lower pedicels in the cluster remaining 

 normal. In the majority of cases this gall is terminal, but in a few in- 

 stances the stem was found to project a short distance beyond it. 



"The gall has the relatively simple structure of a spindle-shaped 

 enlargement of the stem. In length it varies from 10 to 15 mm. and 

 in greatest width from 5 to 8 mm. It is roughened on the outside by 

 the stumps of the aborted branches. On account of the shortening of 

 the stem axis and the consequent crowding of the nodes, these branches 

 are more numerous on a gall than on a corresponding length of normal 

 stem. This gives the gall a gnarled surface and forms a strongly pro- 

 tected case for the larva. The gall in some cases is surmounted by a 

 tuft of leaves growing from its apex. 



"The aperture through which the moth escapes from the gall is made 

 always near the upper end." — Cosens. ^^ 



