PREFACE vii 



" 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 



