MOUNTAIN TREES 



The oaks and the roses seem to have 

 been specially chosen by the gall-mak- 

 ing insects for home-sites. Any day's 

 hunt will reward you with a half dozen 

 forms each as individual and curious as 

 can be. Most familiar of all are the oak 

 "apples" so long prized by the ancients 

 as a remedy in disease. These abnormal 

 growths so rosy and round are often so 

 numerous as to make the injured tree ap- 

 pear laden with fruit. They are due to 

 the irritation of the plant tissues by the 

 tiny larvae of Cynipid gall-flies. By 

 some extraordinary and curious instinct 

 the female selects certain sites most 

 adapted for the production of the gall 

 and with her awl-like ovi-positor pierces 

 the tender growing tissues of the leaf or 

 twig and there lays her eggs. In two or 

 three weeks tiny footless larvae are born 

 and begin to feed upon the sap of the 

 vascular plant tissue in which they lie 

 embedded. Then with the salivary se- 

 cretions and physical irritation produced 

 by the larvae as the exciting cause, the 



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