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 
known as the cambium layer or the cambium region. 
“The cambium itself is a clammy secretion, formed in 
the spring; a highly viscous fluid elaborated by the 
internal organs serving to nourish several parts of the 
plant ” (Henslow, ‘ Dict. Bot. Terms,’ p. 32). 
“The cambium layer is a tissue in which a very 
vigorous formation of new cellsis carried on” (Kerner 
and Oliver, ‘The Natural History of Plants,’ vol. 1, 
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 
inwardly, and from the cortex, by the phloém out- 
wardly. 
The xylem is that portion which has developed, or 
will develop into wood cells; the phloém is that portion 
