V. 



On the /Etiology and Life-History of some 

 Vegetal Galls and their Inhabitants. 



THIS paper is to be regarded as of a preliminary character, merely 

 treating of the subject of galls in its more popular aspects. 

 It embodies the results of observations made by the writer in his 

 scanty leisure of the past twenty -five years. 



With regard to their origin, galls (in the restricted sense in 

 which the term is here applied) are complex organisms, resulting from 

 the co-operation of a plant and an animal ; and to determine the extent 

 and modus operandi of these two factors in their production is one of the 

 many interesting problems which this study suggests, but for the 

 solution of which no complete answer can as yet be given. Why, for 

 instance, from the action of one species of insect, a large, irregular 

 excresence should be produced ; or why, from that of another, a 

 smooth, spherical gall, or a scaly bud, or a circular disc, is a mystery 

 which, for the present at least, science is powerless fully to unravel. 

 It is, however, but a special instance of the universal problem, as to 

 the cause by which normal organic structures are produced in normal 

 organisms. 



Though abnormal with regard to the plant, inasmuch as their 

 presence is exceptional and foreign to the performance of its proper 

 functions, galls, in themselves, are nevertheless as normal as any 

 other organisms. Each has its own characteristic form, its special 

 habitat, and its proper office. 



Composed at the outset, like all vegetable growths, of cellular 

 tissue, galls undergo more or less modification as they pass through 

 the several phases of their life-history. Some, at maturity, are hard 

 and woody ; others soft and succulent. Their colours are bright red, 

 or green, russet-brown, or white, or yellow ; with, oftentimes, such 

 nice gradations and harmonious blendings of all these, as to give to 

 them the aspect of ripe fruit or quasi-flowers. Though, as a rule, 

 more or less globular in form, their shapes vary considerably. Some 

 are smooth and regular, others rough and amorphous. In one, we 

 have the form of an elongated cone ; in another of a cup or goblet ; a 

 third is urn-shaped ; a fourth discoid ; a fifth reniform. Some, as 

 the oak-apple, are composed largely of a mass of spongy parenchyma ; 



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