2 6 British Vegetable Galls 



{b) Mantle galls. These are hollow, in a multiplicity of 

 forms, and have for a lining a portion of the surface of the 

 affected organ, and in many cases a cavity or open communi- 

 cation. 



{c) Solid or tubicular galls, in which a spot is pierced by 

 an insect and the ova deposited in the tissues, not on the 

 surface. These differ from mantle galls in that there is no 

 cavity nor opening, the imago having to bore its way out. 

 They are, however, subject to numerous modifications. 



The other group is composed of compound galls, and com- 

 prises those in which several plant-organs are concerned in 

 the production. They are arranged according to structure, and 

 named scroll, pocket, and covering galls. 



It will now be necessary to review these various methods of 

 classification, in order to form a judgment as to which is the 

 least involved, and at the same time the most efficient. 



I. According to the natural order in the animal world of 

 the creature which causes the growth and issues therefrom. 



It is not in every case possible to determine from the gall 

 alone what creature has caused its growth, more especially in 

 the case of galls found for the first time by the gallist, or new 

 to science. The difficulty of keeping the gall in a living con- 

 dition until the emersion of the tenant has to be overcome. 

 And supposing this to be successfully accomplished, not the 

 rightful inhabitant issues from it, but parasites, inquilines, and 

 hyper-parasites are very frequent, and the difficulty of assigning 

 them to their respective families is considerable. Sometimes 

 the rightful inhabitant itself dies within the gall. Yet another 

 difficulty presents itself: the larvae of many species leave the 

 gall to pupate either some distance away or in the earth, and 

 they invariably die when kept under artificial conditions. 



II. According to the botanical order of the plant upon 

 which the gall grows. 



A classification of galls under this head is too elaborate. 

 There are about a hundred natural orders into which the 

 British flora is divided. An arrangement based upon so many 

 sections is suitable only for a very large and comprehensive, 

 world-wide collection. 



III. According to the situation of the gall upon the various 

 organs of the plant. 



