SOHIZONEURIN^. 85 



coustruction effected by various species, wliicTi greatly 

 helps the student in separating kinds, the diagnosis 

 of which is obscure. This assistance also may be 

 claimed in distinguishing the Scliizoneurince. 



Thus we have all varieties of form, from the simple 

 folding of the leaf to the open bladder-like blistering 

 of the surface, and from the pedunculated gall and 

 the large hollow purse of Schizoneura lanuginosa to 

 the complicated and fruit-like form constructed by 

 Ghermes, in which the excrescence exactly mimics the 

 fir-cone with all its bracts. 



The causes of these diversions of growth and modi- 

 fication of structures in the leaf into such remarkable 

 adaption for a purpose, has engaged the attention of 

 many. The subject is a large one and of high interest, 

 but as it pertains more correctly to the science of 

 vegetable Teratology, only passing allusions and 

 remarks will be permissible in this Monograph. 



It may be noted that the injection of acrid or other 

 juices into living vegetable tissue by Hemiptera and 

 other insects, produces in plants phenomena very simi- 

 lar to inflammation in animal organisms. Vessels be- 

 come turgid, cell-walls become thickened, and abnormal 

 growths (in vegetables often elegant instead of mon- 

 strous) take the place of simpler structures. 



Some writers have thought that ail insect galls are 

 modifications of either fruit or leaf buds,* but many 

 forms cannot satisfactorily be referred to the malfor- 

 mation of originally normal buds. The " mimicry " 

 of fruit observable in some kinds is very remarkable, 

 and these probabl}' point to such an origin ; amongst 

 which, as an Aphis production, may be noticed the 

 above-mentioned gall of Ghermes abietis. It is only by 

 cutting into such structures that we can distinguish 

 their nature from a true fruit. 



The oak galls, known as oak-spangles, the work of 

 JSfeuroterus Malpigii, and those fabricated by Sjyathe' 



* Vide Mr. A. Wilson on tlie growth of galls, 'Nature,' vol. xx, 

 p. 55. 



