28 THE EXISTS OP GRAINS IN THE UNITED STATES. 



P. graminis hordei (stem rust of barley) on barley, wheat, and rye. 



P. graminis secalis (stem ruyt of rye) on rye and barley. 



P. graminis avenae (stem rust of oats) on oats. 



P. rubigo-vera tritici (leaf rust of wheat) on wheat. 



P. simplex (leaf rust of barley) on barley. 



P. rubigo-vera secalis (leaf rust of rye) on rye. 



P. coronata (leaf rust of oats) on oats. 



(7) Two biologic forms may inhabit the same cereal or cereals (for instance, wheat 



and barley rusts on wheat and barley) without being identical. 



(8) By gradual variation and adapta,tion to varying conditions a certain rust spe- 



cies, widely distributed, may form a number of strains or types, differing in 

 physiological reactions. 



(9) The host plants exercise a strong influence, not only on the i^hysiological and 



biological relationships, but in some cases even on the morphology of the 

 uredospores. 



In regard to the relationships of the cereal rust forms to the numer- 

 ous grass rusts of the United States there is much to be done. A 

 beginning has been made, and experiments have been performed 

 confirming Carleton's results (30, pp. 55, 61-63) in regard to the infec- 

 tion of Hordeum juhatum with the stem rusts of wheat and barley 

 and orchard grass with the stem rust of oats. That Agropyron repens 

 also acts as host for the stem rust of wheat has been proved. The 

 relationship of Puccinia phlei-pratensis to other rusts has been inves- 

 tigated and a summary of results published (59, p. 791). The 

 importance of this phase of the biologic forins of cereal rusts is very 

 great and demands early attention. The most extensive results 

 obtained up to the present time are those of Carleton with the 

 American and Eriksson with the European rusts. ^ 



THE .ffiCIDIAL STAGE OF RUSTS. 



HISTORY OF BARBERRIES IN RELATION TO RUST. 



Up to 1864-65, when De Bary demonstrated the heteroecism of 

 Puccinia graminis Pers., rust life histories were very incompletely 



1 During the course of preparation of this bulletin several important papers have appeared throwing 

 further light on biologic forms of rust. J. C. Arthur ("Cultures of Uredineaa in 1909," Mycologia, vol.2, 

 no. 5, 1910, pp. 227, 228) cites experiments of his o\^^l showing that Puccinia pociiliformis (Jacq.) Wettst. 

 {P. graminis Pers.) has been growTi on Triticvm vulgarc from a?cidiospores derived from inoculations on 

 Berberis vulgaris with teieutospores from Agropyron repens, A. tcncrum, A. psnidorcpens, Agrostis alba, 

 Cinna arundinacea, F.lymus canandensis, and Sitanion longifoUum, respectively. lie concludes that 

 "although in the uredinial stage this nist shows racial strains that inhibit the ready transfer from one species 

 of host to another * * * yet in the acial stage racial strains play no part, and the barberry acts as a 

 bridging host between each and every other gramineous host." 



Jaczewski, on the other hand, in a recent article (Zeitschrift fiir Pflanzenkranklieiten, vol. 20, no. fl, 

 1910, pp. 3ot), ,357) cites comprehensive inoculation experiments to show that the stem nists of grains and 

 grasses in Russia as a nile are not interchangeable even witli the barberry as a bridging host, but retain 

 distinct physiological specialization in the a'Cidial as well as in the uredo stage. lie also shows that the 

 aecidia produced from inoculations with the teieutospores from the stem rusts of wheat an<i barley, respec- 

 tively, behave differently when used for inoculat ion on the same series of grains and grasses, and he believes 

 it ea.sily jjossible that the stem rust on barley is a distinct jiliysiological species, a conclusion independently 

 derived in another way by the writers of this bulletin (pp. 17-20 and 2.5-27). Although it is evident from 

 the experiments citea by Arthur that the barberry may act as a bridging host for rusts between some 

 gramineous hosts, in the light of the work of .Taczewski and others it seems that further experimentation 

 on a large number of rusts is neces.sary before the sweepingstatement that "in the a>cial stage racial strains 

 play no part" can be generally accepted. 

 1.'16 



