CROWN ' RUSTS ' 737 



by a ring or crown of blunt teeth (B, Fig. 249), hence the name 

 crown 'rust.' 



-P. coronifera attacks oats only among cereals, but biological 

 modifications occur on foxtail, rye-grass, tall fescue, Yorkshire 

 fog, and other grasses. The uredo-sori are small, of orange 

 colour, and chiefly present on the upper surface of the oat leaf. 



The secidiospores are produced on Buckthorn (Rhamnus 

 caiharticus, L.). 



P. coronata does not occur on cereals, but is common on 

 couch-grass, Yorkshire fog, Fiorin and other grasses. Its 

 tecidia (Fig. 248) are formed on Black Alder {Rhamnus 

 Frangula L.). 



Prevention and Remedies. — At present no satisfactory 

 method is known for the prevention of the enormous annual 

 loss of cereal grains due to the attacks of ' rust '-fungi. Neither 

 spraying the crop nor pickling the seed-grain have hitherto 

 proved of any practical value in combating the parasites. 

 The following means for reducing the prevalence of rusts 

 among cereal crops are, however, worthy of careful considera- 

 tion. 



(a) Avoid the excessive use of nitrogenous manures, for 

 experience shows that 'rust' is always liable to be severe in 

 a crop grown with heavy dressings of dung and nitrate of soda. 

 A judicious application of phosphates is especially necessary to 

 counteract the prejudicial eifects of nitrogenous manures when 

 the latter have been applied in superabundance. 



(j)) As dampness of soil and atmosphere favour the develop- 

 ment of rust, good drainage should be secured as far as possible. 



(c) The plants barberry, alkanet, bugloss and buckthorn, upon 

 which the aecidiospores of the different species of Puccinia are 

 produced, should be eradicated, although the effect of this 

 practice in many instances appears to be slight. 



{d) Cereals sown early in spring are found to suffer less from 

 ' rust ' than those sown later. 



3A 



