396 



The Museum Gazette 



Oak. 



Oak leaves with the small button-like galls of Neuroterus 

 lenticularis (a small fly) on veins on the under-surface. By 

 absorbing the sap these galls have caused the death of the 

 leaf above them. The galls have fallen away from some 

 leaves, but the absence of bilateral symmetry in the brown 

 markings clearly indicates that the decay is not induced by 

 senility. 



Oak. 



Oak leaves for the most part withered and brown, but 

 retaining green patches here and there. A gall of Neuroterus 

 fumipennis occupies (on the lower surface of the leaf) the 

 centre of each patch of green. (Compare with beech leaves 

 showing similar chlorophyll patches.) 



Group III.— CHANGES INDUCED BY FUNGUS PARASITES. 



Bramble. 



Bramble leaves attacked by a rust fungus, Phragmidium bid- 

 bosum. (a) Upper surface with bright red spots. The leaf 

 does not show autumnal colouring, (b) Under-surface of the 

 same leaf, with corresponding spots ; these are purple red, and 

 the dark centre of each is a ripe spore mass, (c) Leaf showing 

 senile colour changes, together with the red spots induced by 

 the parasite. 



Dogwood. 



Leaves of dogwood (Cormis sanguined) with purplish spots 

 induced by a parasitic fungus, Phyllosticta comicola. Similar 

 markings occur on Viburnum leaves. It is not an uncommon 

 fungus. Other species of Phyllosticta attack living leaves of 

 fruit trees, and of celery. 



Sycamore. 



Sycamore leaves with large black spots caused by the 

 fungus Rhytisma acerinum, a very common parasite. The 

 spores rest over the winter and attack the young leaves in 



