148 BEITLSH OAK GALLS. 



Galls caused by the Fungus Dichaena quercina, Fries. 

 (Plates LXV, LXVI.) 



Position of gall. — On twigs, brandies and stems of Quercus 

 pechinridata, and Q. sessUiflora. 



Synonym of fungus. — Opegraph quercina, Pers. 



This remarkable fungus gall-formation is frequently 

 seen on stub-oaks by the road-side. Hedges, that are 

 periodically trimmed, are the best to search for 

 specimens. The fungus also affects young trees in 

 woods, where it forms masses of considerable size ; but 

 trees of more than about fifty years old appear to be 

 less frequently attacked. In some districts it is very 

 abundant. 



jN^ot much is known about the habits of the fungus. 

 Spores settle in a crack or wound in the bark, and 

 when germination takes place the mycelium works 

 its way into the cambium layer and the pith, sets up 

 irritation, and consequent multiplication of cell tissue. 



The earliest indication of attack is seen in a slight 

 rounded swelling of the bark, smooth and gloss}^ This 

 continues for a long time. It affects the smallest twigs, 

 also thick branches, and the stems. 



The swelling of the affected part is very slow, and 

 it is some years before the epidermis yields to the 

 pressure of abnormal growth beneath it and splits, 

 mostly in a transverse direction to that of the twig. 

 The coraceous appearance of the excrescences is 

 peculiar to this fungus ; they are solid and hard. 



The parallel and concentric ridges of projection, 

 correspond with the number of annular rings in the 

 branch. 



The fungus probably lives for a great number of 

 years. Except when very abundant on a bush or 

 tree it does no serious injury. 



