312 Transactions of the Canadian Institute [vol. ix 



Dimensions: — As the size of the gall varies with that of the stem, 

 an average of several specimens was taken. Length, 60 mm.; width, 20 

 mm. ; diameter of normal stem at place of location of the gall, 12 mm. 



A cross section of this gall, when compared with the normal stem, 

 shows an abnormal thickening of the cortex and an increase in width of 

 the bast and wood. Throughout the annual rings of wood are bast 

 fibres, sometimes arranged irregularly in patches, in other cases forming 

 fairly definite zones on the outside of the annual ring. The fibres are 

 shown in Fig. 16. 



Eucosma scudderiana Clemens. 



"The galls are at the top of the main stems of the plants, usually 

 within the flowering panicle, rarely on the branches of the panicle; 

 usually but one gall on a plant, occasionally two, rarely three. 



"The galls are spindle-form, varying in size from 10X16 mm. to 

 12X28 mm.; diameter of stem below gall from 4 mm. to 5 mm.; the 

 average of ten galls collected in ten seasons, 100 specimens, was 9^X21^ 

 mm., diameter of stem below gall 5 mm. " — Brodie.^^ 



The gall mass in this case is produced from the vascular bundles 

 and the intervening parenchymatous strands. When the larva enters 

 the stem it first eats out the pith. After the exhaustion of this source of 

 nourishment, its food is supplied by the radial thickening of the bundles 

 into the gall cavity. The secondary w^ood elements thus formed remain 

 somewhat parenchymatous and can scarcely be distinguished from the 

 cells of the medullary rays. The cortex is somewhat thicker than that 

 found in the normal stem but this is not a very marked feature in the gall 

 production. 



In the normal stem of Solidago canadensis L. there is a gland opposite 

 each bundle both on the side of the cortex and on that of the pith. The 

 glands in the cortex of the gall are the same in number but are very much 

 larger (Fig. 21). Likewise they are not regularly arranged but grouped 

 two or three together. This is due to the fact that since some of the 

 bundles have developed much more rapidly than others, their alignment 

 has been destroyed. 



The glands corresponding to the normal inner row were not found 

 in the gall. This is accounted for by the early removal of the pith of 

 the stem by the producer larva. 



Gnorimoschema gallasolidaginis Riley. 



"Galls usually on the lower third of the stems of Solidago cana- 

 densis L. occasionally on the upper third, rarely at the summit of the 

 stem. The galls vary in form from spindle-form to prolate and oblate 

 spheroid; and in size from 10X21 mm. to 18X30 mm. 



