ON A FUNGUS DISEASE OF EUONYMUS JAPONICUS LINN. F. 437 



growth of the tree." Prof. Shotaro Hori sent examples collected at Nishiga- 

 hara, Tokio, July 12, 1904. 



It seems, then, more probable that the fungus may have been lately 

 brought to Europe on diseased plants imported from Japan than that a 

 European species of Oidium has of late years spread from its original host 

 and attacked E. japonicus as a new host-plant. On the former theory we 

 find an explanation of the fact mentioned above, viz. the epidemic 

 character of the disease now beginning to be shown by the Oidium in 

 Europe, since it is an established fact that a parasitic fungus on reaching 

 a new country attacks its host- plant with exceptional virulence for several 

 years after its arrival. Examples of this phenomenon have been seen in 

 the historic case of the Vine-mildew, and also in that of the American 

 Gooseberry-mildew, recorded in the last number of this Journal. As 

 Bubak (3) has pointed out, it is probable that the importation of diseased 

 Apple trees into Bohemia has recently been the cause of the introduction 

 into that country of the Apple-mildew. 



In those countries in which the Government most fully recognises the 

 economic importance of vegetable pathology — as in the United States and 

 New Zealand — the adoption of precautionary measures for the avoidance 

 of fungus diseases has been enforced by legislation. In such countries 

 the passing of Acts framed to prevent the introduction into the country of 

 plant-diseases affecting orchards and gardens has safeguarded the interests 

 of the fruiterer and horticulturist, in the same way as those of the animal- 

 breeder have for a long time been protected by the various Acts prohibiting 

 imports of diseased or suspected animals. 



The earliest date of the occurrence of the disease in England, of which 

 I have received information, is the year 1900, when the mildew was 

 noticed by the gardeners on the shrubs of E. japonicus trained up against 

 the wall at the east end of the Shelter Terrace in the Madeira Road, 

 Brighton. The disease soon spread to the west end ; and the fungus is 

 now, as I observed myself in the autumn of 1904, extremely abundant on 

 the plants along the whole sea-front for over a mile. It is noticeable that 

 the disease is worst in places where the shrubs are growing in shaded, ill- 

 ventilated situations. In such places the shrubs are often so virulently 

 attacked that the fungus causes the premature falling of many of the 

 leaves ; it also affects the chlorophyll in the leaf-cells in the neighbour- 

 hood of the mycelial patches, producing a mottled appearance on the worst- 

 affected leaves. During the particularly wet summer of 1903 the fungus 

 was very prevalent in many gardens at Bexhill ; * in 1904 it occurred in 

 great quantity at Hastings, Rauisgate, and Felixstowe, and was also 

 noticed during the same year at Sandwich, Folkestone, Woodnesborough 

 near Dover, Iford, and Lewes. 



With the object of gaining information as to the present distribu- 

 tion of the disease in Britain, I sent dried examples of leaves bearing the 

 fungus to the leading firms of nurserymen in the South and North of 

 England and in Scotland, asking whether the disease was known to them. 

 With the single exception of a firm in the South of England, the fungus 

 was not known. The firm of nurserymen referred to wrote as follows : 



* A correspondent writes : " Working gardeners inform me that they do not 

 remember having seen the disease in the neighbourhood before the summer of 1903." 



