5§ 



The Museum Gazette 



an example of a-shell slug, the Testacella haliotidea. sent from 

 Torquay. The shell-slugs differ from ordinary slugs in having 

 a shell on the tail. They are carnivorous and feed upon earth- 

 worms, which they pursue in their burrows ; hence may be 

 considered as gardeners' friends. 



A GILBERT WHITE PAGE. 



{Continued from p. 27.) 



The curious effect of insect attacks in stimulating the 

 growth of certain parts of the plant which they have 

 damaged may be found illustrated in hundreds of instances. 

 We have just mentioned the pine-apples on the spruce fir, but 

 the currant gall on the male catkin of the oak is yet more 

 striking. In this case a structure which is naturally very 

 shortlived has its vigour enhanced and its life prolonged by 

 the presence of the parasite. In this instance the fly attacks 

 the pollen-bearing flowers and deposits its eggs. These 

 flowers would, in the ordinary course, wither and fall as soon 

 as the pollen has ripened and been blown away. Under the 

 stimulating influence of the larvae, however, sap is attracted, 

 their stems thicken and become fleshy, and instead of 

 withering, they produce what looks like a handsome bunch 

 of currants. 



Another instructive instance of parasitism stimulating 

 growth may be observed at this season in any patch of the 

 common field thistle. Some of the plants are almost sure to 

 be affected by a parasitic fungus. It is present in the stole 

 of the plant, and its influence will cause the affected plants 

 to put forth leaves earlier than the healthy ones. They will 

 also grow faster, and in the course of a month be twice the 

 height of their fellows. The fungus grows in the stem, and 

 finally it will flower out on the surface of the leaves. When 

 this happens the plant will die, but up to that period its 



