470 Journal of Agricultural Research voi. x, no. 9 



The results of inoculations with P. graminis tritici compacti can be 

 summarized as follows : 



Hosts on which the rust has been found in nature: Agropyron smithii 

 Rydb., Elymus catiadensis h., E. condensatus Presl., E. glaticus Buckley, 

 E. macounii Vasey, Hordeum juhaium L., Triticum compactum Host. 



Hosts easily infected by artificial inoculation: Agropyron cristatum 

 J. Gaert., A. elongatum Host., A. tenerum Vasey, Bromus tectorum L., 

 Hordeum vulgare L-., Triticum durum Desf. (some varieties), Triticum 

 monococcum L., T. vulgare Vill. (a few varieties). 



Weakly infected by artificial inoculation: Agropyron desertorum 

 Schult., A. intermedium Beauv., A. repens (L.) Beauv., Secale cereale L., 

 Triticum dicoccum Schr., T. durum Desf. (some varieties), T. vulgare 

 Vill. (most varieties tried). 



Artificially inoculated but not infected: Agrostis alba L., A. sto- 

 lonijera Vasey, Alopecurus geniculatus L., A. pratensis L., Anthoxanthum 

 odoratum L., Avena sativa L., Holcus lanatus L., Koeleria cristata (L.) 

 Pers., Phleum pratense L., Poa compressa L. 



It is quite evident that this rust is very similar in many respects to 

 P. graminis tritici. However, its behavior on most varieties of Triticum 

 vulgare so far inoculated is so very different from that of P. graminis 

 tritici that it can scarcely be included in the latter form. All of the 

 hard spring wheats, including Minnesota 169, Minnesota 163, Marquis, 

 and Preston, are very resistant to P. graminis tritici compacti, showing 

 a high degree of hypersensitiveness, while they are very susceptible to 

 P. graminis tritici. (See PI. 53-56.) The same is true of the hard winter 

 wheats which have been inoculated. The soft wheats are, however, 

 more susceptible. It is on account of its very distinctive action on the 

 hard wheats of the vulgare group that it seems desirable to apply a dis- 

 tinct name in order to avoid confusion. The morphology of the ure- 

 diniospores is also somewhat different from that of any of the other 

 forms. 



P. tritici compacti has been found only in the Palouse country, where 

 it seems to be very common on wild grasses and on club wheats. Whether 

 ordinary P. graminis tritici also occurs in that region, the writers have not 

 yet been able to determine. All the rust collected on wild grasses and 

 cereals was the tritict compacti form. 



The degree of stability or fixity of the rust should be thoroughly in- 

 vestigated. It is possible that it is an easily ^hanged variant strain of 

 ordinary P. graminis tritici, although all attempts made by the writers 

 to change its parasitic tendencies by confining it for a number of suc- 

 cessive generations to an uncongenial host or by the use of possible 

 bridging hosts have been unsuccessful. 



