J. Smolak 153 



of investigations by Reynolds are to be considered as galls (viz. 

 mycocecidia) according to the terminology of Kiister. 



Changes similar to those which occur in Prunus leaves are 

 w< 11-known phenomena also in other galls, whether mycocecidia or 

 zoocecidia. Enormous hypertrophy of the nuclei may occur in all 

 galls and may attain sometimes unusual dimensions. The nuclei of 

 the host plant under the influence of Synchytrium (Guttenberg, 4, 

 p. 438) may become 250 times the volume of the normal nuclei. "An 

 enlargement of the nucleus often to double the normal size and often 

 a change of shape to spindle form" was observed also by E. F. Smith 

 (16, ii. p. 92) in plant organs attacked by bacterial disease. Also 

 "septum-like" nuclei similar to those which occur in diseased Prunus 

 leaves were established by Guttenberg in Alnus incana attacked by 

 Exoascus amentorum (after Kiister 7, p. 202). The pathological nature 

 of the amitosis and also the forcing of chromatin grains toward the 

 periphery of the nucleus, have already been pointed out. 



Not only the cytological characteristics but even the anatomical 

 features of the silvered leaves investigated show a cecidiological nature. 

 The study of histogenesis of galls has shown that the abnormal growth 

 of host cells is a symptom of all galls. In the case of the Silver-leaf 

 disease the hypertrophy of the mesophyll is perhaps not very marked, 

 but yet it is quite obvious from a comparison of healthy and affected 

 mesophyll. A similar hypertrophy of the mesophyll was noticed by 

 Kusano in the leaves of Vicia unijuga attacked by Olpidium Viciae 

 Kus. : " The mesophyll of the diseased spot is hypertrophied with the 

 enlargement and the increasing number of cells" (6, p. 177). The 

 falling asunder of mesophyll cells which has been previously noted in 

 the silvering leaves by all authors appears also in the leaf-gall of Oligo- 

 trophus bursarius on Glechoma (Kiister, 7, p. 197). Moreover the 

 epidermis ruptures under the influence of Synchytrium Taraxaci, as 

 already stated. 



If we review the comparisons just mentioned we must admit that 

 the affected tissue in the case of Silver-leaf behaves as a parasitised tissue, 

 and on structural grounds belongs to the category of gall-tissue, using gall 

 in the ivider sense of the word. It is true that there is no characteristic 

 common to all galls, but every pathological feature of the Silver-leaf 

 disease finds a parallel in some gall. 



Although the study of the etiology of Silver-leaf disease lies beyond 

 the scope of this contribution yet one etiological deduction was of 

 necessity forced upon one during this investigation. According to the 



