104 The Galls of Essex ; a Contribution to a 



growth of the normal organ affected by the gall the more 

 short-lived the abnormal formation. In other words, the 

 most quickly matured species of galls are always on the 

 short-lived organs of reproduction rather than on the slow- 

 growing organs of vegetation. For instance, in the oak, 

 compare the catkin galls with the root and stem galls — the 

 growth of Spathe(jaster baccarum galls with those of Aj)liilothrix 

 Sieboldi, for instance. In the galls of S. baccarum I have also 

 noticed that the growth is quicker in the catkin form than in 

 the leaf form; the spring bud galls (e.g., Spathefjasteraprilinus, 

 Aphilothrix albopunctata, &c.) grow and mature much faster 

 than the autumn galls [Aphilothrix globuU, Andricus 

 gemmcB, &c.). 



In the galls of the Cynipidse we thus know that, soon after 

 the deposition of the egg, active animal growth commences ; 

 this immediately sets up irritation of the plant-tissues, and 

 according to the subtle specific character of the irritation and 

 the nature of the part of the plant acted upon, the particular 

 morbid or hypertrophied growth is produced and is main- 

 tained by an increased influx of nutritive material. This 

 growth, however, only continues during the active life of the 

 tenant ; for as soon as the irritation ceases, apparently the 

 vegetal growth also stops. This is quite analogous to the 

 action of certain special irritants and the diagnoses of certain 

 inflammatory actions in causing (Edematous swellings in 

 animal organisms, the different eflects and nature of each 

 being well known ; as with the multifarious forms of galls the 

 cause and effect are patent, but the subtle differences 

 occasioning such constant but diversified results are un- 

 traceable. In the animal kingdom, hypertrophy or thickening 

 of the cuticle is known to occur as the result of continued 

 pressure to any part; but a less pronounced form of hyper- 

 trophy of cuticle is seen in the various forms of warts, where 

 pressure is not an immediate agency in their production. 

 I believe no intelligible explanation of the cause of warts and 

 similar excrescences in the animal kingdom can be given ; it 

 is so with the vegetable galls, but in this kingdom we well know 

 that the growth of the cambium tissue, &c., is accelerated 



