322 Transactions of the Canadian Institute [vol. ix 



Cecidomyia triticoides Walsh. 

 "On Salix cordata Muhl. A polythalamous woody gall .70-1.23 

 inch long and .30-. 37 inch in diameter, bearing a remote resemblance to 

 a head of wheat with the kernels elongated, naked, pointed and very 

 protuberant, its general outline oval or elongate-oval, and formed by the 

 swelling of a twig to 2 or 3 times its former diameter, the swelled portion 

 being very much contracted longitudinally, so as to bring each kernel- 

 like bud nearly or quite into contact with the base of the one that pre- 

 cedes it in the same row, the whole number being arranged in four irregu- 

 lar rows." — Walsh.** 



The larval chambers in this gall are placed us'ually along the line of 

 the fibro-vascular bundles of the stem, and wherever a chamber is situ- 

 ated the vascular tissues are not developed. 



An examination of a young stage of this gall shows that nearly the 

 whole of the pith and cortex of the stem consists of a well defined aeri- 

 ferous tissue. It is absent in only a few cell layers that surround the 

 larval chambers. Represented in Figs 34, 35, 36. At this stage there is 

 a well differentiated protective sheath, of about five cells in depth, 

 around each larval cavity. The cells of this layer have uniformly thick- 

 ened walls and are arranged in concentric rows around the larval chamber. 

 Each cell of this zone contains either a crystal aggregate or a well defined 

 single crystal of calcium oxalate. Inside of this protective sheath is a 

 nutritive layer which consists of about six rows of thin-walled cells. 

 The cells of this zone have the same tangential arrangement as those of 

 the protective sheath. Many of them are empty, this being especially 

 the case in the innermost row. Likewise, many are commencing to 

 collapse on account of the withdrawal of their contents. These zones 

 are represented in Fig. 38. 



A section of a gall at a much more advanced stage of development 

 presents several important differences. The aeriferous tissue is very 

 much compressed in the pith and somewhat in the cortex. The cell walls 

 of the protective zone are now much thicker, and a well defined crystal 

 of calcium oxalate completely fills the lumen of each cell (Fig. 37). 



Weidel" has recorded a phenomenon similar to this occurring in 

 the gall Andricus cortids Hart. 



"Oft ist das ganze an sich schon grosse Zellumen durch einen ein- 

 zigen Kristall ausgefiillt, dem anscheinend so ansehnliche Zellulose- 

 massen spaterhin waren sie verholzt, aufgelagert worden sind, dass diese 

 die Wand des Behalters erreicht haben und mit ihr verwachsen sind." 



My observations differ in one respect from Weidel's, namely, there 

 is no ensheathing mass of cellulose around the crystals found in the gall 

 dealt with here. In deciding this point tests were made at different 

 stages with Schulze's solution. 



