. Une contribution à la morphologie et la biologie des tumeurs d'insectes [microform]. Le Galles (botanique) ; les galles (botanique). 19'aj morphologie et biologie des tumeurs d'insectes 349 cellules à paroi mince, illustré en Fig. 68. Les écailles des bourgeons entourant ce groupe de cellules proches de celles des bourgeons normal sauf que la cuticule de l'épiderme est anormalement épaissi. Euura S. ovum Walsh. "Sur Salix cordata. Un ovale ou rond, monothalamous swelhng, sessiles, de 0,30 à 0,50 pouce de long lengthwxys, placé sur le côté de petites brindilles, vert où qu'elle est lisse, mais essentiellement couverte de fissures peu profondes et irrégulières longitudmal

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. A contribution to the morphology and biology of insect galls [microform]. Galles (Botany); Galls (Botany). 19'aj Morphology and Biology of Insect Galls 349 thin-walled cells, shown in Fig. 68. The bud scales surrounding this group of cells resemble those of the normal bud except that the cuticle of the epidermis is abnormally thickened. Euura S. ovum Walsh. "On Salix cordata. An oval or roundish, sessile, monothalamous swelhng, .30 to .50 inch long, placed lengthwxys on the side of small twigs, green wherever it is smooth, but mostly covered with shallow longitudmal cracks and irregular rough scales which are pale opaque brown. Its mtemal substance fleshy in the summ-r like that of an apple but with transverse internal fibres. When rip3 in the autumn filled with reddish-brown spongy matter, with close-set transverse internal fissures at right angles to the axis of the twig. On cutting dowTi to the twig at any time a longitudinal slit about .30 inch long becomes plainly visible."â Walsh.** As already noted the host of this gall in this locality is Salix humUis It remains to be determii.d .whether there are two distinct species of producers or one species with two hosts. Walsh's description of the gall on Sahx cordata corresponds to the form occurring here on 5. humilis. The ovipositor of the producer has in this case made a longitudinal cut in the stem. A transverse section at the place where the gall is located showfi that this wound extends in Trom the epidermis to the boun- dary of the pith. The activity of the young tissues, abnormally stimu- lated, soon fill this fissure with a mass of small, angular parenchyma The rapid division of these cells forces the exposed edges of the cortex and central cylinder apart so as to form a wedge-shaped opening which is filled up with the gall mass (Fig. 71). It should be stated that the newly formed cells originate mainly from the division of a cambium bordering the pith at the bottom of the fissure. But other tis

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