(314: [December 



that the microscope shows nothing about them, externally or internally, 

 indicating that an insect has anything to do with causing them," and 

 maintains that they " are not of insect origin, nor a vegetable fungus, 

 but are properly a disease of the tree, analogous to bhe cancer in the 

 human body." {ibid. pp. 21 — 2,) yet I cannot help believing that the 

 •' Black-knot," as well as the " Curl," is the work of (lall-gnats. It is 

 perhaps presumptuovis in one who has never specially investigated the 

 subject, to set up his own opinion against that of a distinguished natu- 

 ralist who has devoted considerable attention to it ; but there is an old 

 saying that " bystanders sometimes see more of the game than the 

 players themselves," and it may be the case that a general acquaint- 

 ance with many allied species can sometimes supply the place of the 

 most laborious special investigations. 



My reasons for the belief which I have just avowed are the follow- 

 ing : — 1st. Just as Curculionidous larva are inquilinous in the Cecido- 

 myidous galls Q. pilulse Walsh and S. semen n. sp. and others are in- 

 quilinous in the galls of other Gall-gnats, (see above p. 607. and be- 

 low under Colropfera), so the common Curculio (ConotracheJns 7irmi- 

 phar Hbst.) is notoriously inquilinous in the Black-knot. Dr. Fitch, 

 for example, says, that the ■ larvae of the Curculio are almost always 

 found in them" {Rep. Cure, and Bl. Knot. p. 21). and Harris says that 

 they are '-sometimes" found there {Inj. Ins. p. 80.) Again, just as I 

 have bred 8 distinct inquilinous Lepidoptera from various Cecidorayi- 

 dous galls on the Willow, so Dr. Harris states that •• the naked cater- 

 pillars of a minute moth are very common in the Warts of the Plum 

 tree," {Ibid.) and I have myself found there their pupal exuviae. 2nd. 

 The general appearance of the Black-knot is very similar to that of the 

 Cecidomyidous gall, ^S*. batatas n. sp.. and like that gall it is said to 

 be •• spongy" inside, when young and immature. On examining, Dec. 

 4th, 30 — to dead and dry specimens, I find that, besides some larger 

 holes through which the Curculio and other inquilines have probably 

 made their escape, they are perforated externally by several round holes, 

 proportionally about I as numerous as in the above Willow-gall when 

 it is a year old. and only .020 — .025 inch in diameter, which is a trifle 

 smaller than they are in that gall. Now this size is altogether too small 

 for the larva of the Curculio — though it certainly suits well enough for 

 that very rare parasite of the Curculio. Siyalphus eurculionis., which 



