The Galls of Essex. 99 



Galls are known to occur on plants in nearty every order 

 of the vegetable kingdom ; they vary greatly in their form 

 and in thejr situation on the plant. This will be fully 

 exemplified presently, when I shall come to a detailed 

 examination of our Essex gall fauna. 



More strictly speaking, the term "gall" is applied to an 

 abnormal vegetable growth. Lacaze Duthiers defines "galls " 

 as comprising " all abnormal vegetable productions developed 

 on plants by the action of animals, more particularly by 

 insects, whatever may be their form, size, or situation."^ 

 This is by no means a scientific definition, but the limitation 

 is convenient and the intention is apparent. It must, 

 however, be remembered that all abnormal vegetable growths 

 are not galls, as will readily be seen from a study of Dr. 

 Masters's 'Vegetable Teratology.'^ 



This brings us to a starting point — the cause of galls. A 

 gall is an abnormal vegetable growth produced through the 

 internal action of some foreign agency. This agency is 

 generally either the influence of a fungus or of some 

 Arthropod. Certain of the AnguillulidaB,^ belonging to the 

 Nematode worms, and some Infusoria {Vibrio, &c.), are also 

 gall-makers, and possibly even certain Kotifera. Both the 

 animal and the vegetable causative actions produce often 

 remarkably similar inflammatory and stimulated growths, 

 and most frequently these are abundantly distinct from any 

 normal production or growth of the galled object. 



So far the subject is clear, but the exact way in which the 

 foreign influence is brought to bear on the vegetable growth 

 is still matter for conjecture and experiment. The actual 

 progressive structure of the gall itself also still affords a good 

 working field for the structural botanist. 



The "gallic" force of an insect, so to speak, is vulgarly 



2 ' Annales des Sciences naturelles.' Botanique. 3rd series, vol. xix., 

 p. 273. Paris, 1853. 



3 'Vegetable Teratology.' By Maxwell T. Masters, M.D., F.L.S. 

 London (Bay Society), 1869. 



4 ' Monograph on the Anguillulidae.' By H. Charlton Bastian, M.A., 

 M.B. Transactions of the Liunean Society, vol. xxv., pp. 73 — 184, 

 pis. 9—13. (1866). 



