1908.] 



Rust in Wheat. 



243 



plant they can flourish upon. A knowledge of this fact is of 

 great value, for it shows that the spread of rusts from one crop 

 to another need no longer be taken into consideration when 

 attempting to check the progress of one of these parasites. 

 For all practical purposes one might as well expect potatoes 

 to become attacked with apple canker as wheat to be infected 

 with the rust from barley. 



Undoubtedly the most important species of rust in this 

 country is the yellow rust, Puccinia glumarum. This appears 

 without fail each season, in some years in such abundance 

 that the whole of the foliage and even the ears and grain 

 become coated over with its orange-yellow spores. The black 

 rust, Puccinia graminis, is often stated to be the common rust 

 of the country, particularly by writers to the popular press. 

 As a matter of fact it is so rare, at all events in the eastern 

 counties, that in most seasons I have failed to find it amongst 

 standing crops, and in order to obtain material for teaching 

 purposes and investigation, special crops of it have had to be 

 grown by artificially infecting late sown wheats. In many 

 other parts of the world, in Canada, the United States, the 

 Transvaal and Australia, for instance, this species is the 

 prevalent rust, and its attacks are so virulent that the crops 

 occasionally fail completely. It is thus a matter to be thankful 

 for that this species is comparatively rare here. 



The life history of the yellow rust appears to be more simple 

 than that of many other species. It is generally first noticed 

 in some abundance in the early spring, though in some seasons 

 it does not put in an appearance in quantity until late in May. 

 Then small yellow patches, about one-sixteenth of an inch 

 across, are found scattered about on the foliage. Under favour- 

 able conditions these increase in number with great rapidity, 

 often becoming confluent and forming long narrow stripes. 

 Each patch then becomes powdery on the surface owing to 

 the breaking of the skin of the leaf and the setting free of 

 myriads of orange coloured spores known as " uredospores." 

 Any one of these which comes into contact with the leaf or 

 stem of a healthy plant may bring about infection and produce 

 a fresh crop of thousands of new uredospores in the course of 

 some 10 days. Any one of these new spores may in turn 

 repeat the process, so that it is possible for even a single fleck . 



Q 2 



