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BRITISH OAK GALLS. 



CHAPTER I. 

 THE PRINCIPLES OF OAK GALL FORMATION. 



The part of the tree from which the material is 

 supplied to build up the substance of a gall is that 

 knowu as the cambium layer or the cambium region. 

 " The cambium itself is a clammy secretion, formed in 

 the spring; a highly viscous fluid elaborated ])y the 

 internal organs serving to nourish several parts of the 

 plant " (Henslow, ' Diet. Bot. Terms,' p. 32). 



" The cambium layer is a tissue in which a very 

 vigorous formation of new cells is carried on " (Kerner 

 and Oliver, ' The Natural History of Plants,' vol. i, 

 p. 475). It may also be described as "a series of 

 formative cells lying outside of the wood proper and 

 inside of the inner bark. The growth of new wood 

 takes place in the cambium, which is very soft " 

 ('Webster's International Dictionary,^ p. 207). The cells 

 of which it is composed form a complete thin cylinder 

 concentric to the pith throughout the whole of the 

 plant, but separated from the pith by the xylem 

 inw^ardly, and from the cortex, by the phloem out- 



co w^ardly. 



— The xylem is that portion which has developed, or 

 ^ will develop into wood cells ; the phloem is that portion 



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