14 THE BUSTS OF GRAINS IN THE UNITED STATES. 



R. caroliniana Walt., and R. cathartica L. The exact relationship of 

 the American and European crown rusts can be determined only by 

 parallel inoculation experiments with European and American forms. 

 These have not yet been performed. 



Leaf rust of rye. — In Europe the leaf rust of rye (Puccinia dispersa 

 Erikss.) forms its ascidium on Anchusa officinalis L. and Lycopsis 

 arvensis L. Arthur (11, pp. 236, 237) succeeded once in growing the 

 spermogonia of the American form (Puccinia rubigo-vera secalis 

 Carleton) on L. arvensis L. in this country. It is believed, therefore, 

 that the American and European forms are identical, but further 

 experimental evidence should be obtained. 



Leaf rust of barley. — Leaf rust {Puccinia simplex (Korn.) Erikss. and 

 Henn.) of barley was not reported in the last bulletin on rust issued 

 by this Bureau and seems, in fact, not to have been previously re- 

 ported. The American form agrees in all morphological character- 

 istics with the European form. It is chiefly characterized by the pre- 

 dominance of the one-celled teleutospores. The teleuto stage is often 

 somewhat scarce. The earliest collection of this rust available for 

 examination was obtained in Iowa in 1896. It was collected in Cali- 

 fornia in 1905. It has been noticed in abundance, especially toward 

 fall, chiefly on volunteer or very late barley, in Minnesota during the 

 seasons of 1905 to 1908, in Maryland in 1910, and was reported in the 

 spring of 1906 from Virginia, where it occurred in great abundance, 

 but, like the leaf rust of wheat, it caused little appreciable damage. 



BIOLOGIC FOBMS. 



General Discussion. 



Rust fungi exhibit great variety in regard to complexity of life his- 

 tories. Some are confined to single-host species, others range over 

 two or more species of one host genus, while still others range over two 

 or more genera and often on different tribes of the same family. This 

 comprehensive range may obtain in addition to the alternation of host 

 plants, as in the stem rust of cereals. For instance, the stem rust of 

 oats passes its aecidial stage on barberry, while the uredo and teleuto 

 stages may be found on practically all species and varieties of oats 

 and on several grasses, some of which are not at all nearly related to 

 oats, but are, in fact, genera of tribes somewhat removed from that 

 of the oat (30, pp. 61-63). Attention must be called to the fact that 

 the ranging to other species occurs most abundantly in the uredo and 

 teleuto stages, though it is not unknown in the aecidial stage. Fur- 

 ther complexity arises in the following way: What may appear to the 

 the eye, and often under the highest power of the microscope, as one 

 and the same species of rust on a number of species, or even varieties, 



216 



