J. Smolak 155 



It is, however, not at all certain that Slereum purpureum is really 

 responsible for the Silver-leaf disease. Indeed we find in the literature 

 concerning the subject of this disease a considerable amount of doubt. 

 At the beginning of this paper various views respecting the etiology 

 of this disease were pointed out. Massee (9, p. G6) has failed to find 

 any hyphae in affected plants. Even Brooks has not found Stereum 

 in all cases of this disease. This author examined some silvered plum 

 seedlings which were growing from seeds obtained from healthy trees, 

 and he states : " The silvering was strictly comparable with that which 

 occurs in adult trees. The epidermis was partly free from the under- 

 lying palisade tissue and on trying to cut sections of the leaf there was 

 a decided tendency for the mesophyll cells to fall asunder one from the 

 other. There was no evidence of fungal attack in either leaf, stem, 

 or root. As already stated, the seedlings began to recover when given 

 more room in which to grow and upon examining them in August, 

 I saw that the recovery of the foliage to its normal appearance was well 

 advanced. I came to the conclusion that in such a case as this the 

 phenomenon of Silver-leaf was not caused by Stereum purpureum''' 

 (Brooks, 1, p. 291). Or on the contrary: " . . .cases have been already 

 mentioned in which Silver-leaf has not resulted although Stereum 

 purpureum has made considerable progress in the tissues. I have 

 seen apple and beech trees which have been killed by Stereum 

 purpureum in all probability, but with which the phenomenon of 

 Silver-leaf has not been associated" (Brooks, 1, p. 307). In the light 

 of this evidence it is not possible to believe that Stereum purpureum 

 is the sole cause of the Silver-leaf disease! Perhaps the inoculation 

 experiments hitherto carried on have been too few or possibly they 

 are not yet complete enough to decide the relation of Stereum to this 

 disease. In Bohemia the same external phenomenon, viz. the silvering 

 of foliage, has appeared frequently in recent years on the leaves of sugar 

 beet (Beta vulgaris). Of course we must not draw conclusions here 

 from the similarity of the external symptoms, nevertheless it seems to 

 me that the study of this affection, which of course is not caused by 

 Stereum, may possibly explain some obscure points connected with the 

 Silver-leaf disease in trees. 



Further studies on the cytological changes occurring in diseased 

 plum leaves would be of value. The changes found in leaves in the 

 spring should be studied. Besides the phenomena above described 

 I found bacteria in the diseased plum leaves ; thus occasionally in the 

 cells of the parenchyma bordering on the vascular bundles or in the 



