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BRITISH GALLS 
certain infective forms of inflammation, and perhaps to 
some forms of tuberculosis. It is impossible to exclude 
them by any definition; at the same time their compre¬ 
hension under the name of “galls” will probably be 
very inconvenient and productive of much confusion. 
They should, I think, be allowed to constitute a separate 
group, and with them should be placed the diseases 
known in England under the name of “ canker.” 
A gall in its special but now well-recognized meaning 
of the word may be defined as a growth on a plant or 
tree caused by the deposit of an insect egg in process of 
development, or by the presence of a fungus. The 
special kind of gall produced will depend upon the 
endowments of the part in which the irritation occurs, 
and will vary not only with the kind of plant, but with 
the minute details of vital endowment of the part. 
Thus it will be influenced by the precise part of the 
stem, leaf, or bud which is attacked. The conditions 
which are favourable to galls of all kinds are active 
vitality on the part of the plant, free supply of sap to 
the special part affected, and seasonal conditions of 
warmth. 
The Oak, of all trees, produces probably not only the 
greatest variety of gall structures, but the greatest 
abundance of individual forms. 
It must be acknowledged that there is much in refer¬ 
ence to peculiarities in different galls which is as yet ill 
understood. There is no doubt that the nature of the 
gall produced is influenced not only, although chiefly, 
by the special endowments of the plant attacked, but 
also by the character of the irritation which attacks it. 
