86 THE REPORT OF THE No. 19 



and Basswood, but sometimes it more nearly encircles the branch or twig. 

 In form it is irregularly oval, about ^ to | in. long, I to ^ in, wide and | to ^ 

 in. high. The texture is pit-like. The surface, at first smooth and like 

 that of the bark, grows rougher as the gall matures. Polythalamous. The 

 larvae are greenish, about 3 mm. long and 1 mm. thick. It occurs, usually, 

 singly but often with two united in a straight line, on the terminal branches 

 of the American Aspen (Populus tremuloides). Fairly common at Guelph. 



The Willow Potato Gall (Rhabdophaga batatas, 0. S.) Plate A., fig. 7. 

 An oblong ovate gall about 1 in. in length and J to | in. in thickness. 

 The surface is irregular, but for the most part fairly smooth. The color is 

 similar to that of the bark at first, but turns gray when mature. The texture 

 is pith-like, but fairly hard. The gall is polythalamous. The larvse are 

 small and pinkish. It occurs singly usually. But sometimes with two or 

 more in close proximity on any part of the twigs of the Scrub Willow (Salix 

 sp.). Common. 



Cock's Comb Hawthorn Gall (Hormomyia cratosgi folia, Felt). Plate 

 A, fig. 4. 



This gall is very similar io the Cock's Comb Gall on the Elm (Colopha 

 ulmicola). It is on the upper surface of the leaf and has the appearance of 

 two tiny leaflets about 4-6 mm. high and 8-10 mm. long growing up parallel 

 to each other but at right angles to the surface of the leaf. The upper margin 

 of each is crenate usually, but sometimes the two leaflets coalesce at the top 

 and become thickened in this part. They are green in appearance and of the 

 same texture as the rest of the leaf. On the under surface, there is usually 

 a considerable depression or groove on each side of the base of the gall. Of 

 the infested leaves examined, none had more than two galls to a leaf. Mono- 

 thalamous ; contains a single white larva tinged with yellow. Occurs on the 

 Hawthorn {Cratcegus sp.). Rather rare. 



Elm Leaf -fold Gall. (Cecidoviyia ulmi, B^euten.) Plate A, fig. 1. 



The gall takes the form of a pulpy thickening of the tissues in the under- 

 surface of the leaf, extending for some distance along the midrib. It is 

 usually near the base of the leaf, and causes the upper surface to double on 

 itself instead of expanding in the ordinary way. The enlargement varies 

 in length from about \ tol in. and usually extends about \ in. on each side of 

 the midrib. It is about 2 mm. thick. The surface is pubescent like that of 

 the rest of the leaf, but is more or less irregular, with ridges and hollows, 

 often appearing as though two or three galls were joined together. On the 

 upper surface of the leaf the pocket found opposite to the enlargement on 

 the lower surface contains several small white larvse which have a slight pink- 

 ish tinge. The gall occurs on the American Elm (Ulmus Americana). 

 Fairly common this year, 1907. 



Balsam Fir Needle-Gall. (Cecidomyia balsamifera, Lintner). Plate 

 A, fig. 3. 



This is an irregularly oblong gall, situated near the base of the needle 

 on the new growth. It encircles the needle, is about 3 mm. long, and from 

 1 to 2 mm. thick. The surface in most cases is smooth, though often some- 

 what corrugated, especially on the under surface. The color is a little paler 

 green than that of the needle and the texture somewhat looser and more pulpy. 

 The gall is monothalamous and contains a single orange-colored larva which 

 CAugust 5th, 1907) had not yet begun to pupate. There is usually only one 

 gall to a needle, but sometimes two continuous ones are found. Occurs on 

 the Balsam Fir, {Abies balsamea). Rare. 



Dogwood Leaf Gall. (Lasioptera corni, Felt.)._ Plate A, fig. 2. 



Thin-walled circular elevations on the under side of the leaves of Cor- 

 mus. Somewhat bladder-like in appearance, and sometimes occurring in 



