COLOURS OF GALLS. 311 



Botanists and physiologists will see that this idea is quite 

 groundless, but to the uninstructed and popular mind it has a 

 sort of plausibility that often commands assent. But when we 

 come to the oak-tree the case is at once altered, and some other 

 cause must be found for the lovely colours of its galls. The 

 cherry-galls are as brightly coloured as any apple, and the soft 

 hues of the oak-apple are nearly as beautiful though not so 

 brilliant. Yet the oak possesses no such store-house of colour 

 as is popularly attributed to the rose. Its leaves are simple 

 green, and its flowerets are so colourless as scarcely to be dis- 

 tinguished by the unassisted eye. 



Whence then are derived these beautiful colours ? Some hasty 

 observers, who have neglected the first rule of logic, and drawn 

 an universal conclusion from particular premises, have said that 

 the colours of the gall are derived* from the insect: adducing, 

 as a proof of their assertion, the brilliant colours which equally 

 deck the rose-bedeguar and the Cynips rosce. from which it sprang. 

 But if they had only followed the example of careful naturalists, 

 who, like Dr. Hammerschmidt, have examined and drawn be- 

 tween two and three hundred species of galls, so hasty a gene- 

 ralisation would never have been made. The cherry or leaf-gall 

 of the oak is every whit as gorgeously coloured as the bedeguar 

 of the rose, while the insect that made it is quite black. Tt is 

 true that the diaphanous wings glitter as if they were made of 

 polished gems ; but this appearance is due, not to the wings 

 themselves, but to the myriad hairs with which they are regu- 

 larly studded, each hair acting as a miniature prism by which 

 the light is refracted and broken into the resplendent hues of 

 the rainbow. 



Many other trees besides the oak are chosen by certain species 

 of gall-fly, and even the herbs and flowers do not escape the 

 ravages of these remarkable insects. The white poppy, from 

 which is obtained the opium of commerce, is attacked by a 

 species of gall-fly, which lays its eggs in the large head, or pod, 

 and sometimes does much damage to the plant, the delicate 

 divisions between the seed-vessels being rendered quite hard 



