What is a Vegetable Gall? 7 



of oviposition, and not to the functions of the parts of the 

 plant upon which they develop. There is a remarkable similarity 

 of form in the galls produced by the EriopJiyida;. 



The larvae of some species of the same genus of insects 

 cause galls which are totally unlike each other. Urophora 

 cardui deposits ova in the young shoot of the thistle, and a 

 succulent, glabrous, external swelling develops. U. solstitialis 

 oviposits in the flower of Centaurea Tiigra, and the result is 

 a very hard, hirsute formation completely obscured by the 

 florets. Rhodites nervosus oviposits in the under surface of a 

 rose leaflet, and a unilocular, globular, pedunculated larval 

 chamber grows therefrom ; but R. spinosisshnce performs the 

 same operation, and the leaflet itself bulges out on both 

 surfaces to so great an extent that the serrations of its 

 margins are scarcely perceptible. Other instances of the same 

 phenomenon will present themselves to the collector in the 

 course of investigations. 



No kind of British vegetable gall appears to be of any 

 service to man in arts or manufactures ; nor are they suitable 

 for food. Birds do not eat them, but when food is scarce in 

 winter time, the small birds (Tits) remove the woody exterior 

 of several kinds to get at the larva, which is then devoured. 



About 270 kinds of British vegetable galls are known. 



Reference may here be made, and illustrations introduced, 

 to show various growths on plants known as glands, lenticles, 

 etc., which are like galls and are misleading to the novitiate 

 gall-collector. They are not due to parasitic agency, and do 

 not contain ova or larvce. The glands on petioles of Pnuius 

 avium (plate 2) are well defined. 



Glands as formed on plants are of various shapes and sizes, 

 and of four principal kinds. They occur mainly on the various 

 parts of the leaf, and appear in the form of sessile or pedun- 

 culated, wart-like bodies, or embedded in the tissues of the 

 plant, and occasionally contain a resinous or oily substance. 

 A rather loose cellular tissue without epidermis is one of 

 their chief constituents. 



The tuberous formations of petioles and roots of various 

 plants demand a passing notice. 



Among the pond weeds there are several whose underground 



