CHAPTER XXIII 

 FUNGI 



SILVER-LEAF DISEASE (Reports, VI, 210; XII, i) 



SILVER-LEAF, or silver blight (Stereum purpureum), is a disease 

 which has long been known to fruit growers in this country : 

 it manifests itself by the foliage of the affected trees becoming 

 light and silvery in appearance ; a tree thus attacked often 

 dies, though death may not supervene till after several years, 

 and, while suffering, it may still bear a certain amount of 

 fruit, and may even show considerable vigour of growth. This 

 silvering of the leaves was first connected with fungoid action 

 by Professor Percival, 1 who attributed it to the action of 

 a fungus known as Stereum purpureum, which fructifies only 

 on the dead wood of a tree killed by the attack. Apparently 

 the mycelial threads of this fungus, which penetrate the 

 cells of the living tree, and thus bring about its death, are 

 very fine, and the difficulty experienced in discovering them, 

 coupled with the fact that the fungus never fruits on the wood 

 till after death, resulted in Professor Percival's conclusions being 

 looked upon with some scepticism. Independently of his results, 

 however, those obtained at Woburn would be quite sufficient 

 to place the matter beyond doubt ; for the inoculation of a tree 

 with a piece of the fungus has nearly always been found to produce 

 silver-leaf, whilst neighbouring trees which were not thus inocu- 

 lated remained quite healthy. Further, trees which have died, 

 partially or entirely, after an attack of silver-leaf, so often develop 

 the stereum on the dead wood, that it is impossible to avoid 

 connecting the one with the other, especially as no single instance 

 is on record of the appearance of this fungus on a tree which has 

 been known to have shown no signs of silvering whilst alive. 



The fungus itself forms flat, roundish disks on the bark of 

 the dead wood, often two inches or more in diameter, and 

 generally shows a purple or pink colour, though sometimes it 

 is nearly white (Fig. 23). For the purpose of inoculation, it is 



1 Linn. Soc. Journ., "Botany," 35, 390, 1902. 

 231 



