Diseases of Cereals : Bust nud Take -all in Wheat. 715 



2. The spores which are produced iu such immense numbers may 

 serve to carry it on from season to season. They are light and easily 

 carried by the wind, and it has been shown that they exist in the air 

 as well as on the ground. It is quite common in some seasons for 

 one's clothes to be quite red with the spores in passing through a 

 field of wheat, and at threshing time the air is filled with them. In 

 colder countries than ours, these red spores are supposed to lose their 

 germinating power during the winter but with us it is retained till 

 next season. It is very common to find spores entangled in the 

 bearded tip or '' brush" of the grain, and these would form a starting 

 point for the rust. 



3. This rust appears on about 20 grasses in xA.ustralia, and it is 

 generally considered that they may serve to harbour it after the 

 wheat is reaped, but it is not always certain that the spores would 

 infect the wheat. It has been shown, however, experimentally that 

 some, such as the barley grass {Hordeum murinum), can do so, and 

 it is good farming practice to keep down such weeds as much as 

 possible. 



Self-sown wheat is regarded as another means whereby the rust 

 may be continued throughout the year, so that it is advisable to feed 

 it down with sheep. 



4. There is another possible way in which the rust may be carried 

 over from one harvest to another, and that is by means of the seed in 

 which it may be hereditary. This view has been prominently brought 

 forward by one who has devoted considerable attention to the study 

 of rusts in Sweden, viz., Professor Eriksson. He considers that Avhile 

 infection by spores does occur, the primary infection comes from 

 within from an internal germ of disease inherited from the parent 

 plant and latent in the seed. He has not yet succeeded in giving 

 scientific proof of his theory, but he considers that this view explains 

 the origin of outbreaks better than any other. 



It used to be taken for granted that the rust appearing on wheat, 

 oats, and barley was interchangeable and that it could readily pass 

 from one to the other. But infection experiments have shown that 

 this is not the case, that the rust on each of these three different 

 species of cereals seems to have acquired a special liking foi' a 

 particular species and now they confine themselves to their own 

 choice. Only in the case of wheat-rust it is found that its choice is 

 not yet so definitely fixed as the others and that its spores can in rare 

 instances impart the disease to oats and barley. But between the 

 two latter there is a distinct barrier and the spores from the oats will 

 neither infect wheat nor barley, nor will the spores from the barley 

 infect wheat or oats. It follows from this that adjacent fields of 

 these crops will not affect or be affected by each other, so far as 

 this rust is concerned. This fact had already ])een noticed by 

 observant farmers, for one wrote to me as follows : — " I have never 

 found rust to spread from one field to another, as two years ago I had 

 60 acres of oats rusty, while 50 acres of wheat adjoining were free, 

 the oats receiving heavy rain while in blossom, while the wheat 



