356 Transactions of the Canadian Institute [vol. ix 



branches are given off without the formation of intercepting walls. It 

 seems to represent an exaggerated form of the spongy parenchyma. 



Proliferation of glandular tissue is shown in Aulacidea nabali Brodie. 



Cynips? constricta Stebbins furnishes an example of an outer accessory 

 nutritive zone that clearly assists in supplying the larva with nourishment 

 (Fig. 54). 



Notes on the Protective Zone. 



This zone is typical for the Cynipid galls, but as already stated it is 

 differentiated in certain Dipterous forms, such as Rhabdophaga batatas 

 Walsh (Figs. 25, 26) and Cecidomyia triticoides Walsh (Figs. 37, 38), and 

 also in the Hemipterous gall Pachypsylla celtidis-mamma Riley (Fig. 15). 



In the Cynipidae it usually bounds the nutritive zone on the outside, 

 but it does not invariably occupy that location. When two layers are 

 present the inner occupies that position, but the outer is situated nearer 

 the periphery of the gall. 



The term, "protective," has been applied to this tissue without a 

 very clear idea as to what it protects from. The common notion appears 

 to be that it forms an inner line of defence against parasites and small 

 animals other than insects. The latter class of enemies appears to inter- 

 fere very seldom with galls. Cook^^ mentions one example — he found 

 birds tearing open the galls of Pemphigus vagabundus Walsh. Very few 

 examples of such cases have come under my notice. Galls of Holcaspis 

 bassetti Gillette are occasionally opened by woodpeckers, and the larvae 

 of Eurosta solidaginis Fitch are sometimes taken from the galls by field 

 mice. Chipmunks will also tear open the galls of Pemphigus rhois V\'alsh 

 to get at the inhabitants. Not only are galls seldom attacked by such 

 animals but a sclerenchymatous tissue would be a very poor defensive 

 device against them. 



Adler^ has advanced the idea that this zone protects against insects 

 that are parasitic on the producer-larva. This appears very unlikely 

 since the parasites oviposit at a comparatively early stage, and the scleren- 

 chyma is differentiated relatively late in the development of the gall. 

 The same writer cites the large size of the gall and the thickened epidermis 

 as other protective devices against parasites. The same argument is 

 applicable in this case ; the gall is not large nor is the epidermis abnormally 

 thick at the time the parasites are ovipositing. Were Adler correct the 

 gall Amphibolips confluens Harris should be almost immune against 

 parasites, as it is large, has a thick epidermis and a well-developed pro- 

 tective sheath. In spite of all these apparent advantages this gall has 

 a heavy casualty list owing to .parasitism. During last season hundreds 

 of this species were opened and on an average about 75% were found to 



