354 



NATURAL SCIENCE. Nov. 



others, like the woolly gall of the oak, are surrounded by a thick 

 coating of cottony-down ; while in the case of the Bedegnar of the rose, 

 we have a tangled mass of branching-filaments, compact yet free, and 

 so compressible as to have obtained for this gall the names of the 

 " Rose-Sponge" and " Robin's Cushion." 



Few plants, it is said, are altogether free from these parasitic 

 growths. Of those indigenous to Great Britain, a list of over 150 

 gall-bearing plants has been given. Such growths are found alike 

 upon trees and shrubs and herbs. No organ escapes their deleterious 

 presence. They appear on root and stem, on branch and leaf, on 

 bud and flower, and fruit. 1 Every part, in turn, pays tribute to the 

 invaders. 



Of our native plants, the Oak (which is especially rich in varied 

 forms of animal-life) produces the greatest number and variety of 

 galls. From the oaks of Central Europe Dr. Mayr has described and 

 figured ninety-eight specific galls.- Upon those of Nottingham and the 

 immediate neighbourhood I and my friend, Dr. W. H. Ransom, 

 F.R.S. (to whose initiative I owe my early interest in this subject), have 

 noted some twenty-nine or thirty, out of a total of forty-one known 

 British oak galls ; while upon a single leaf I have counted more than 

 2,300 distinct gall " spangles " — those of Nearotevus lenticularis. 

 Though many tumour-like galls are due to the action of parasitic 

 fungi, Acaridae, and other as yet imperfectly classified organisms, 

 the great majority are produced by various orders of Insecta. Among 

 these, the busiest gall-makers are found among the Cynipidae (or Gall 

 flies), and the Tenthredinidae (or Saw-flies), two subsections of the 

 Terebrant Hymenoptera. The galls of these insects are (so far as I 

 know) invariably closed galls, from which the larvae, in some cases, 

 and in others the imago — then furnished with mandibulate jaws — 

 eat out their way, when mature, and escape. 



In the case of the Cecidomyidas (or gall-midges) and other 

 families of Diptera, as well as among gall-producing Aphides — all of 

 which have suctorial mouths — the galls, on the other hand, though 

 in most instances closed for a time, decay or dehisce so soon as the 

 contained insect has reached a stage when its exit from the gall 

 becomes necessary ; but for this wondrous adaptation and provision, 

 the home of the little occupant would, of necessity, become its prison- 

 house and grave. 



Limiting now our attention to a few only of the typical galls 

 referred to, let us endeavour to trace out some of the more salient 

 features of their life-history. 



And first, of the " Oak Nut," or " Marble gall," as it is some- 

 times called. This is a simple, unilocular gall, due to the puncture 

 of Cynips lignicola of Hartig, or Cynips kollavi of Geraud, the largest 



1 Malpighi, quoted by Reaumur, vol. iii., p. 418. 



2 " Die Mitteleuropaischen Eichengallen," 1870. 



