Excitatory Emanations. xxxix 



that the gall-mother injected any irritating secretion 

 whatever, and Beyerinck ^ proved that the fluid ejected 

 by the gall-fly is without taste or smell, and absolutely 

 unirritating if injected under the skin. It is probably 

 nothing more than a very mild antiseptic dressing 

 applied to the wound made in the plant. Both these 

 authors show plainly that it is not in the gall-mother, 

 but in the larva, that we must seek for the cause of 

 gall-growth; and that it is the nature of the salivary 

 secretion, and the manner of feeding of the larva, 

 peculiarities inherited by each species, which give the 

 characteristic growth to the gall. The fact that some- 

 times a blastem has actually begun to form before the 

 egg-shell has ruptured, proves that one of the exciting 

 causes must be a chemical fluid, secreted by the salivary 

 glands, and possessing amylolytic and proteolytic 

 ferments. This fluid is capable of passing through the 

 cell-walls and producing effects at a distance of several 

 mm. beyond actual contact with the larva-. 



The necessity for the continuance of the excitation 

 during the whole period of gall-growth is shown by its 

 cessation when the larva has perished by parasites. 

 In some galls, however, the parasites are evolving the 

 power of prolonging gall-growth beyond the death of 

 the gall-maker, although they have not yet actually 

 acquired the art of initiating it. 



The duration of gall-vitality is shortest in succulent 

 galls, such as Spathcgaster baccaruni, S. albipes, S. tricolor, 

 and S. verrucosus, growing from leaves ; or such as 

 S. Taschenbergi, S. similis, and Trigonaspis ci'ustalis, 

 growing from dormant buds. Galls which grow within 

 the leaf substance, like Spathcgaster vesicatrix and 



* Beyerinck, Uber die crstcn Entwickl. eiuiger Cynipidengallen. p. 179. 

 ^ Hoffmeister. 



