CONTRIBUTIONS FROM THE WISLEY LABORATORY. 489 



next ; and by this means also, if the plants are distributed in the spring 

 with the previous year's diseased leaves attached, the fungus is carried 

 from place to place. 



It is of the utmost importance that, wherever Irises are grown, a 

 very careful watch should be kept for the first appearance of the 

 disease. In the first season the actual damage done may appear 

 small, and fatal neglect may ensue ; for when once the disease seriously 

 establishes itself, as it does in a season or so, its ravages become worse 

 and worse, and its eradication becomes a matter of difficulty. 



All varieties of so-called " German " Irises do not appear to be 

 affected in equal degree. Mr. R. J. Wallis, of Colchester, kindly 

 forwarded me a list in which the strongly attacked varieties are 



Thorbecke Innocenza 



Alcazar Mrs. Darwin 



Chelles Ossian. 

 Darius 



The varieties which were less seriously harmed are 



Gracchus Mrs. Neubronner 



Jacquiniana nepalensis 



Madame Chereau Princess of Wales 



Albert Victor Prosper Langier. 



The varieties least affected are 



pallida dalmatica Victorine. 



Treatment of the Disease. — I am indebted to Mr. F. J. Chittenden 

 for the following account of the Iris disease at the Royal Horticultural 

 Society's Gardens, Wisley : — 



" In 1907 and 1908 the collections of Irises at Wisley were very 

 badly attacked by the fungus Heterosporium gracile. So great was 

 the damage done through the premature death of the diseased parts 

 that the plants were seriously weakened, and at the same time the 

 yellow spotting of the foliage through the attack of the fungus even 

 early in the year made the plants very unsightly. In the latter year 

 an attempt was made to cope with the disease by spraying with 

 copper fungicides, ammoniacal copper carbonate particularly being 

 used, but although the disease was checked to some extent it broke out 

 again in the succeeding year with at least equal virulence. Spraying 

 was again resorted to, the spray being applied every three weeks, 

 but still without curing it. It was evident that the disease could not 

 be stamped out by this means, probably because of (i) failure 

 to wet the waxy leaves with the spray fluid at ail completely, (2) the 

 faculty the fungus possesses of growing on dying foliage, and (3) 

 possibly also upon any organic matter in the soil. The first of these 

 difficulties could have been overcome by adding something to the 

 spray fluid which could dissolve the wax, but this could not be done 

 without some risk of damage to the foliage through the removal of 

 this protective covering. The second and third difficulties could in 

 ordinary circumstances be only partially obviated. 



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