PREFACE 
Vll 
“ nail ” gall on a Beech, or the still more marvellous 
structure of a “ pineapple ” gall on a Spruce, we have to 
observe in all, and especially perhaps in the last, not so 
much the production of new growths as the marvellous 
modifications of special local endowments. The close 
resemblance of the “ pineapple ” gall, which results from 
the presence of the eggs of an aphis, to the cones that 
result from the impregnated seeds of the tree itself, is a 
fact which must ever excite the wonder of the observer. 
It is true that at the outset a certain sentiment of 
repulsion is caused by the fact that the processes which 
we are investigating must be regarded as the results of 
violence, and, in a certain sense, of disease. Whilst 
we learn, however, that there is no protective agency at 
work in Nature which can compel the consistent pro¬ 
gress of any living structure to continue in its apparently 
predestined course, and to protect it against the attacks 
of other forms of life, we find some consolation in 
observing the wonderful and frequently very beautiful 
adaptations which these deranged manifestations often 
assume, and at the same time we are invariably com¬ 
pelled to marvel at the wonderfully varied forms of 
manifestation which “ Nature’s moulds,” under the 
stimulus supplied, can be made to evolve. 
I will confess that I am somewhat reluctant to 
include under the term “galls” certain infectious 
growths, known in America under the name of “ crown 
galls,” about which very interesting information has 
recently been accumulated in the United States. They 
are infective outgrowths, which have but little alliance 
with the rest of the group, and have close alliance to 
