96 SCIENCE PROGRESS. 



of galls has been greatly addc::d to by Beyerinck.^ It was 

 found that in galls produced by Cynipidse, the stimulus 

 which determined the gall-formation did not proceed from 

 the parent, but from the larva. The influence of the latter 

 is exerted even whilst still contained within the egg as is 

 proved by the simple fact that in many cases the eggs are 

 deposited on the surface of the young organs of plants and 

 cemented there, and are then surrounded with a wall by 

 the adjacent tissue. This can only be explained upon the 

 supposition that the larva secretes soluble substances, and 

 that these enter the tissues of the plant. Again, the larva 

 has often been removed from the growing tissue which is 

 being converted into the gall, and indeed in some cases has 

 been separated from the growing tissue by dead tissue, 

 without influence upon the growth of the gall. This shows that 

 the case with which we have to do is not one of propaga- 

 tion of the irritation, assisted by the living protoplasm of the 

 host. Moreover, since the action is a slow one and pro- 

 ceeds from the larva, it may be arrested by killing the latter. 

 Since their growth is interfered with at those points of the 

 young tissues which are in immediate contact with the 

 animal, there is formed a chamber which is always lined 

 with nutriment at the disposal of the larva. As regards the 

 theory of gall-formation, the fact discovered by Adler is of 

 great importance, confirmed as it has been by Beyerinck, 

 that upon one and the same host, the oak, the various 

 forms of a single species of gall-insect produce various galls. 

 The female insects of Dryophante folii, for instance, emerge 

 from their galls upon an oak-leaf in November or December. 

 They immediately look for a bud, a " resting eye," and de- 

 posit an egg upon its vegetative point, a small violet- 

 coloured bud-gall resulting, which, before the connection 

 was known, was ascribed to a gall-insect known as Spathe- 

 gaster Taschenbcrgi. The males and females of this species 

 leave their dwellings in May, and the fecundated female 

 insects deposit their eggs in the veins of young oak-leaves 

 and thereby give rise to the leaf-galls with which we started. 



^ " Beobachtungen liber die ersten Entwickelungsphasen der Cyni- 

 pidengallen," Amsterdam, 1882. 



