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JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



be used wholesale in greenhouses and places where Bordeaux 

 mixture could not be used, on account of the white-wash effect 

 produced on everything with which it comes in contact. 

 Potassium sulphide dissolves most readily in hot water, which 

 should be allowed to cool before spraying. Orchard trees or 

 vines that have been attacked by fungi the previous season may 

 be sprayed with a solution of sulphate of copper — one ounce to 

 three gallons of water — for the purpose of destroying resting- 

 spores. This fungicide can only be used early in spring, before 

 the leaf-buds begin to expand, otherwise the foliage is injured ; 

 hence it cannot be used in greenhouses and places where foliage 

 is present. 



Numerous other preventive methods and fungicides have 

 been proved to be of value in checking specific diseases, but the 

 leading idea of this discourse is to give gardeners an idea as to 

 the varied methods followed by fungi in attacking their victims, 

 and more especially to thoroughly impress on their minds that 

 " prevention is better than cure." 



One group of very destructive parasitic fungi possess the 

 peculiarity of living on two distinct host-plants at different 

 periods of their existence. The too familiar mildew or rust of 

 wheat is an example of this kind, where two conditions of the 

 fungus grow on the wheat-plant, and a third on the leaves of 

 the barberry. Other examples pass one period of their existence 

 on branches of junipers, and another on the leaves of various 

 fruit trees. It is obvious that in those cases where it is 

 necessary for the fungus to pass from one host-plant to another 

 to complete its development, that the removal of one of the two 

 host-plants from the vicinity will arrest the progress of the 

 disease. Various other peculiarities possessed by fungi, which 

 it is impossible to crowd into a single talk on the subject, should 

 be known to gardeners. 



The following illustrations of the mode of attack of well- 

 known forms of parasitic fungi will, it is hoped, enable the 

 previous remarks to be more clearly understood : — 



Orchid Leaf Rust. \ Glwosporium cinctum, Berkl.) 



This is the most generally distributed of fungus parasites 

 with which the cultivator of orchids has to contend. It does 

 not as a rule kill the host-plant, but the leaves are disfigured by 



