410 FUNGOUS DISEASES OF PLANTS 



Host plants. It is scarcely possible to indicate all the various 

 hosts upon which the species, in its various forms, has been re- 

 ported. As mentioned above, however, it attacks all the more 

 important cereals, — wheat, oats, rye, and barley, — together with 

 ordinary grasses belonging to the same genera, in addition to such 

 economic forms as species of Dactylis, Alopecurus, Agrostis, Poa, 

 Phleum, Festuca, and numerous others. 



The important forms or physiological races of this species 

 which have been thus far well established through experimental 

 study are as follows : 



1. Secalis Eriks. & Henn. On Secale cereale, Hordettm vul- 

 gare, Agropyrum repens, Elymits arenarius, Bromns secalinus, 

 and other hosts. 



2. Avenae Eriks. & Henn. Occurring on several species of 

 Avena (including cultivated oats), Agrostis scabra, Alopecurus 

 pratensis, Dactylis glomcrata, and other grasses. Nevertheless, 

 there is some disagreement about some of the hosts upon which 

 this form has been reported. 



3. Tritici Eriks. & Henn. On several species of Triticum (cul- 

 tivated wheats), Hordeum, Agropyrum, and Elymus ; also some 

 other grasses. 



4. Agrostis Eriks. On Agrostis canina and Agrostis stolonif 'era. 



5. Airae Eriks. & Henn. 



6. Poae Eriks. & Henn. on Poa compressa. This form, however, 

 requires further study in order to be sure that it is not more prop- 

 erly one of those already indicated. 



The fungus. This species is of the type euheterouredo. The 

 chief alternate host throughout its usual range is the common bar- 

 berry (Berberis vulgaris). The life history of the fungus may be 

 only briefly outlined, beginning with its appearance upon the bar- 

 berry in the form of the spermogonial and cluster-cup stages. 



The mycelium is septate, considerably branched, and intercellu- 

 lar. It gives rise, however, to small, very slightly differentiated 

 haustoria, which penetrate the cells. The mycelium is distributed, 

 in the case of the barberry, throughout various parts of the leaf. 

 It is, however, in every case localized in areas within a definite 

 range of the point of infection. In the development of the spore 

 stages there is the usual sequence. The spermogonial stage appears 



