192 Silver- Leaf Disease, III 



veins are meant, it must be pointed out. that silvering often proceeds 

 from the leaf margin instead of from one of the larger vascular bundles. 

 With parti-silvered leaves the boundary between the normal and ab- 

 normal jjarts may be sharply defined and may remain fixed, but by 

 marking the boundary with Indian ink, an extension of the silvered 

 area can sometimes be observed. 



Since the publication of Brooks' paper on silver-leaf in 1913 (2), 

 numerous examples of silvered foliage occurring naturally in other 

 plants have been seen. Mention will be made first of those in which 

 silvering was associated with the presence of Stereum purpureiim. 



In July, 1913, our attention^ was called to a number of silvered sloe 

 trees amongst healthy ones in a field hedge near Cambridge. In one of 

 the affected trees some of the branches were dying back. Sections of 

 branches bearing silvered leaves showed sectors of discoloured wood, 

 containing hyphae as described (i, 2) for silvered branches of cultivated 

 plums. The affected leaves exhibited the usual characters of silvered 

 foliage, the tendency of the mesophyll cells to fall asunder being very 

 pronounced. During October of the same year fructifications of Sterewn 

 purpureum developed in abundance on the dead portions of this silvered 

 tree. 



During the summer of 1913 an apricot tree growing against a wall 

 was seen to be silvered and some of its branches were dying back. The 

 leaves showed the usual characters of silvered foliage and the branches 

 that were dying back contained discoloured zones of wood as in silvered 

 plum trees. The silvered branches continued to die during the summer 

 and fructifications of Stereum purpureum arose on them during the 

 autumn. 



Silvering of labvunum trees associated with Steretini pttrpureum was 

 described in the previous paper of this series (2) and it suffices to say 

 that several other silvered trees of the same kind have since been seen 

 associated with this fungus. The frequency of silvering in laburnums in 

 private gardens is probably due to the pruning to which they are often 

 subjected, the wounds so made affording abundant opportunity for the 

 entrance of the wound parasite, Sterenm purpureum-. 



During 1915 many silvered shoots were seen arising from stools of 

 poplar trees and on each of the five stumps from which such shoots 

 arose, Stereum purpureum was growing abundantly. These stools 

 formed part of a row of poplars, the intact trees of which showed normal 



1 We are indebted to Mr F. G. Tutoher, Sub-Inspector of the Board of Agriculture 

 and Fisheries for pointing out these trees to us. 



