12 THE BUSTS OF GRAINS IN THE UNITED STATES. 



regards stem rust, no conclusions are possible from them as to the 

 possibility of epidemic visitation on spring rye. Bolley, at Fargo, 

 N. Dak., during the summer of 1907, had experimental plats of 

 winter r} r e in the vicinity of barberry bushes which were infected 

 with stem rust, and these winter-rye plats were badly rusted. The 

 rust also appeared spontaneously on greenhouse material at Wash- 

 ington, D. C, in 1906. The exact limits of the stem rust are not 

 determinable on account of the meager reports, but it is safe to say 

 that the rust at present is of very little economic importance. On 

 the other hand, it seems probable that it is widely distributed in 

 small quantities. 



Leaf rust of rye. — The occurrence of the leaf rust of rye (Puccinia 

 rubigo-vera secalis Carleton) is coextensive with the culture of that 

 grain, and is often very abundant. It is found everywhere, appearing 

 usually in abundance on the young plants in the fall; in the spring 

 it is ordinarily the first rust to appear on cereal crops. No damage 

 is usually attributed to it, and probably little or none is actually 

 suffered, for the rye matures so early and the rust is so closely con- 

 fined to the leaves that appreciable injury is almost always avoided. 

 As with stem rust of rye, nothing can be predicted concerning the 

 possibilities of leaf rust on spring rye, because comparatively little 

 spring rye has been grown in this country up to the present time. 



BOTANICAL CHARACTERISTICS, LIFE HISTORIES, AND PHYSIO- 

 LOGICAL SPECIALIZATIONS OF RUSTS. 



GENERAL STATEMENT. 



Investigations of recent years have shown conclusively that botan- 

 ical characteristics, life histories, and physiological specialization of 

 parasitic fungi vary to such an extent with the geographical distri- 

 bution that a sequence of forms for one locality is not necessarily the 

 sequence for any other. This brings us face to face with the problem 

 of rust life histories in the United States. Although the European 

 and American forms may be apparently identical morphologically, 

 they are not necessarily identical in their life histories or physio- 

 logical specialization. Investigations on the rusts in this country 

 have shown that while the work of European botanists may be 

 suggestive it can not be accepted as conclusive or final for the rusts 

 of the United States without confirmatory experimental evidence. 

 Some information has been gained in recent years on the specialization 

 of the rusts growing on the different cereals, but much still remains 

 to be done. 



This bulletin represents an attempt to show briefly our present 

 knowledge of these rusts in the United States in comparison with our 

 knowledge of rusts in Europe. For detailed descriptions of the 



216 



