244 



Rust in Wheat. 



[JULY, 



of the disease to prove the starting point of an epidemic. 

 Later in the season, as the plants are beginning to mature, 

 the formation of uredospores ceases and small blackish patches 

 are formed under the skin of the leaf or stem. These are the 

 teleutospores. In the case of the black rust, the teleutospores 

 remain dormant through the winter months and germinate 

 in the following spring to give rise to fresh spores which infect, 

 not wheat, but the young foliage of the barberry, the spores 

 which are then produced on this host plant ultimately infecting 

 wheat and producing black rust on it once more. 



No alternate host plant is known in the case of yellow 

 rust, and it is probable that the fungus does not require 

 one to complete its life cycle. Thus the cutting out of 

 barberry, so often recommended for the prevention of rust, 

 is superfluous where the yellow rust alone has to be dealt 

 with. The uredospore stage seems to be sufficient to enable 

 the fungus to tide itself over the winter, for it is possible to 

 find pustules of rust on the foliage of self-sown wheat or 

 sometimes on the ordinary autumn-sown crop even in the 

 depths of winter. The twisted leaves lying on the soil 

 form a series of sheltered moist chambers on the inner 

 surface of which the rust pustules are occasionally present 

 in great numbers. These may develop with rapidity in the 

 early spring, and at times as early as March the whole of the 

 plant's foliage may be yellow with the rust. The winter's 

 cold does not appear to injure these spores, for they germinate 

 readily when brought into the laboratory, and there can be 

 little doubt that they serve to start the epidemic in the spring, 

 when conditions become favourable for infection. Under 

 these circumstances it is not necessary to assume that the first 

 appearance of the fungus in any season is dependent upon 

 its being actually present in the embryo of the grain, spreading 

 therefrom as the plant develops, and ultimately producing 

 its spores when the external conditions are favourable. 



The actual effects of yellow rust on wheat have received 

 little attention from the economic point of view, though we 

 are familiar enough with them from the botanical stand- 

 point. It is, however, sufficiently obvious that diseased plants 

 cannot produce a full crop of grain. The greater portion of the 

 fungus is deeply imbedded in the host plant, growing chiefly 



