LEAF-MINEKS. 



505 



affected as well as the stem. Fortunately for the gardener, who 

 hates thistles, even though he should be a Scotchman, as is so 

 often the case with skilled gardeners, the larva of the Cleonus 

 feeds on the juices of the plant at the expense of its life, so that 

 the thistle dies just before the seed is developed, and a further 

 extension of the plant is thereby prevented. 



Theke are also gall-making insects among the Diptera. Such, 

 for example, is the Thistle-gall Fly (Jlrophora Gardui), which 

 produces large and hard woody galls upon the thistle, as well as 

 several species of the larger genus Tephritis, some species of 

 which live in the parts of fructification of several flowers, the 

 common dandelion being infested by them. 



LEAF MIXEnS AXD ROLLERS. 



We may now describe, at fuller length than has hitherto been 

 done, another group of insects, which live between the mem- 

 branes of leaves, and which belong to different orders. 



If the reader will carefully examine the leaves of any rose- 

 tree which grows in the open air, he will certainly remark that 

 many of them are notable for certain curious markings, which 

 look something like the rivers in a map, and which traverse the 



