148 BRITISH OAK GALLS. 
Galls caused by the Fungus Dicheena quercina, Fries. 
(Plates LXV, LXVLI.) 
Position of gall.—On twigs, branches and stems of Quercus 
pedunculata, and Q. sessilifiora. 
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. 
Not 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 glossy. 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. 
