BIRCH TREES IN EPPING FOREST AND ELSEWHERE. 283 



The lenticular tubercules consist of black pseudo-parenchyma situated 

 beneath the periderm. Owing to their rupturing the periderm at the highest 

 point of their concave surface, a small depressed aperture is formed." 



The diagnosis of the disease of the birch is ahnost precisely 

 that of Alnits viridis. In each case leafy brandies are infected ; 

 the fungus is with difficulty discerned on the living wood ; the 

 progress of the diseases is indicated by colour ; its highest 

 development is only on the dead wood. Vaisa and Melanconis are 

 very closely allied, as the synonyms quoted above go to prove, 

 and as everyone knows, Betula and Alniis are of the same natural 

 order. 



Granted that Melanconis stilbostonia causes the death of the 

 trees, we can account for the rapid spread of the disease in so 

 many districts several miles apart. The conidiospores carried 

 by the wind, are ready to attack any suitable trees with which 

 they may come in contact, and such a disease as this will be 

 most difficult to cope with on account of the great numbers of 

 trees already attacked. • 



Other causes have been suggested to account for the death 

 of the trees, as drought and overcrowding ; but neither of these 

 bear the test of investigation : for instance, isolated trees like the 

 one in the churchyard at Buckhurst Hill have suffered, and 

 those growing by streams and on marshy localities have died in 

 great numbers. 



There are many questions that suggest themselves to which 

 no answer is as yet forthcoming. For instance, Melanconis 

 slilbostonia has long been known as a saprophyte; has it gradually 

 assumed the habit of a parasite, or was it always a parasite, 

 which has at length become a very formidable tree destroyer ? 

 It is possible tliat its parasitic nature has up to the present L^een 

 unobserved. We have in Cladospoiium epiphylUnn a fungus widely 

 known as saprophytic, but quite recently it has been shown to 

 be the cause of disease and death ot Pyrus japonica (G. Massee, 

 Kew Bnlkiin, Jan., i8gg). This fungus occurs on the living 

 leaves of Betula alba, but the tact is not mentioned in Sarcardo's 

 list of over two hundred species of fungus, known to attack 

 various parts of this tree. 



