TREE MYTHS. 47 



There probably exists a good deal of popular 

 misunderstanding concerning the various ex- 

 crescences found on trees. " Oak-galls " are not 

 plant productions, but are caused by minute 

 gall-flies, and are designed as a protection for 

 their tender offspring before they are able to 

 shift for themselves. Oak-apples are excres- 

 cences of a like nature, divided into a number 

 of cells, each of which contains a grub, a pupa, 

 or a perfect insect, according to season. 



The oak spangles which stud the under sides 

 of leaves were formerly thought to be para- 

 sitic fungi, but are now known to be caused by 

 Gall-flies, as are the tiny spheres attached to 

 the flower-stalk. Myths of a like kind relate 

 to the reddish-coloured protuberances of the 

 leaves of the Lombardy poplar ; while in reality, 

 the tissue thus moulds itself at the working of 

 another species of aphis. But similar popular 

 delusions are almost endless. 



