6 British Vegetable Galls 



There is therefore no warrant for restricting the term 

 vegetable gall to an abnormity, the formation of which is due 

 to cellular structure alone, or accumulation of sap alone, or 

 even to insect agency exclusively, since other agents produce 

 swellings which have the same appearance and cause like 

 deformities of the plant. Nor does the etymology of the word 

 permit such limitations. Henceforth the words must spread 

 over a wider range of meaning — a meaning which can be defined, 

 and a range which can be limited only by the systematist. 



How, then, shall a vegetable gall be described ? What is 

 a vegetable gall? 



It is a morbid enlargement of the affected part of the plant, 

 due to parasitic agency. 



Very few of the higher forms of plants are altogether 

 exempt from the attacks of gall-producers. Fungi and lichens, 

 however, do not appear to be attacked, although there is no 

 apparent reason why these lower forms should enjoy immunity. 

 The formation of a gall takes place only while the plant is in 

 a growing condition ; but the death of the plant is not always 

 an indication that the primary purpose of the gall should cease : 

 so long as sufficient moisture is contained within the tissues 

 of the gall, or that its external crust affords sufficient protection, 

 so long is it fulfilling its main use. Some galls bear no re- 

 semblance to the portion of the plant upon which they are 

 situated ; but there is generally some organ of the plant, modified 

 upon the exterior of the structure, which imparts a distinctive 

 form. The most remarkable illustration of this feature may 

 be seen in the fibrous covering of the Bedeguar gall {Rhodites 

 roses), which represent fibro-vascular bundles of leaves with 

 scarcely any parenchyma uniting them. 



In degree of complexity of internal structure, galls vary con- 

 siderably. Some are quite simple with thin walls — eg. Nematus 

 bellus, in which the larva feeds voraciously upon the interior until 

 it has a mere shell for a covering, and this it leaves to pupate. 

 Other kinds of a more solid nature have several layers beneath 

 the epidermis, and a central cavity in which pupation takes 

 place. Under such conditions the imago is provided with 

 powerful jaws with which to eat its way out. The characters 

 of galls are remarkably constant, and, as a rule, exhibit certain 

 diagnostic features, some of which are obviously due to the act 



