THE BOOK OF GARDENING. 



Leaf-Rust {Puccinia hieracii). — Within the last year or so 

 growers of Chrysanthemums have suffered not a Httle from the 

 ravages of this destructive rust-fungus. In several cases practi- 

 cally whole collections have been destroyed, and in a great 

 many more the loss has been extremely heavy. The generic 

 name at once singles the pest out as a near relative of the 

 much-dreaded Hollyhock fungus, and the specific one suggests 

 that it is not the Chrysanthemum alone that it affects, but the 

 Hawkweeds, many of which are among the commonest wayside 

 flowers. It is necessary — indeed, important — to know this, as 

 it to a certain extent accounts for the transference of the rust by 

 various agencies from weeds to cultivated plants. Nor are the 

 Hawkweeds alone host-plants of the pest. Burdock, Knapweed, 

 Thistle, and Groundsel are quite as commonly infested. 



The rust is found occasionally on the upper surface as well as 

 upon the under surface of the leaves, which after a time are 

 found to be covered with a number of brownish spots of varying 

 size. Sometimes such spots are separate, at others they coalesce, 

 until practically the whole leaf is involved ; finally the leaf 

 assumes a still more unhealthy hue — first yellow and then brown 

 — and falls. Prior to this latter stage, however, the nuniberless 

 spores which have formed have been distributed over an 

 extended surface. Then it is that the parasite is readily carried 

 by insect and other agencies into non-infected areas. In fact, a 

 collection which, say a week or so before, presented a healthy 

 appearance and without the slightest trace of fungus, could 

 practically be ruined in that short time. First one plant, then 

 another, becomes involved, and the collection goes from bad to 

 worse. The actual time occupied by one of the spores in 

 developing, once it has found a congenial resting-place, varies, 

 but from eight to ten days at most would probably cover it. 



Here it may be well to state that the first manifestations of 

 the disease to the gardener are usually the formation of the 

 now familiar rust. Long ere this, however, the insidious pest 

 has been working unseen on the leaf-tissues by means of 

 mycelium. In fact, the "rust" is the outward and visible sign 

 that one kind of fruit has been matured — that known as uredo- 

 spores, or summer spores — and it is by means of this that the 

 area of infestation is increased. And this is where the value of 

 spraying comes in, as it prevents such spores as fall, or are 

 carried upon the foliage, from germinating. 



If spraying with a fungicide be not adopted, then later in the 

 year (towards autumn) another kind of spores are produced. 

 These are named teleutospores. By means of these the plant- 

 disease is usually carried over the winter, though in certain cases 

 it may be continued by means of the summer spores. The 

 grower would therefore be wise to burn such plants before they 

 have arrived at the stage when the winter spores are formed It" 



