242 



two years. For a long time I have noticed that with fruit trees 

 which have been killed by Silverblight, there occasionally 

 appears on the stem or branches some time after the death of the 

 tree the fructification of a fungus; but so much has been said in 

 reference to Silverblight being due to bacteria that I do not think 

 the roundish disc-like fungus growths are connected with Silver 

 leaf disease." Later he adds: " I however forwarded 



specimens to England to a friend, who identifies them as the 

 same fungus which is considered by Professor Percival and others 

 to be the cause of Silver leaf disease of fruit trees in the United 

 Kingdom.'"' The above quotations clearly indicate the scepticism 

 of a number of workers with regard to Percival's discovery. The 

 latter's views were, however, confirmed by Pickering (8) at Woburn 

 during 3906-1909, as the result of a large number of successful 

 inoculations of various fruit trees and a few other trees and 

 shrubs with Stereum purpureum. Similar results, with equal 

 success, were obtained in the detailed work at Cambridge and 

 Merton of Brooks (9). Giissow (10) observed Silver leaf in Canada 

 and repeated with success similar inoculation experiments. The 

 latest contributions on Silver leaf bv Smolak(l 1 ) leave that author 

 still doubtful as to S. purpureum being the sole cause of Silver 

 leaf. He discovered bacteria in silvered leaves, but he con- 

 sidered them of secondary nature. 



In view of the wide distribution of this insidious disease, 

 throughout the continent of Europe, from England to the 

 Balkans, and in America, where, according to Giissow (12) it is 

 prevalent in Canada, from St. John's, Newfoundland to Van- 

 couver Island, and also in Australia and New Zealand, it is 

 plain that Silver leaf is very likely to hamper considerably the 

 fruit growing industry throughout the world unless prompt 

 action is taken to cope with the disease. Unfortunately in 

 England the best varieties of cultivated plums are most sus- 

 ceptible to Silver leaf, a-s can be judged from the plum orchards 

 in Surrey, Middlesex, Kent, and Worcestershire, where in 

 certain plantations 60-95 per cent, of the plum trees of 

 * Victoria " and " Czar " varieties have been so severely attacked 



that wholesale grubbing out of these trees has had to be resorted 

 to. 



The following gives a list of plants known to be affected by 

 Silver leaf : — 



Those marked with * have been observed by the author, those 

 marked *t are new records. 



R 



osaceae. 



*tl. Nevhisia alabamensis, A. Gray. 

 *2. Spiraea japonica var. fflabrata, Lange. 



3. Philadelphus sp. 



4. Exochorda sp. 



5. Pyrus Main* — cultivated varieties of Apples. 



*Lord Grosvenor. Xewton Wonder. 



*Bramlev's Seedlin?. Lord Suffield. 



© 



P. prvni folia. 



P. triloba, Lindley. var. fiore pleno. 



