16 THE RUSTS OF GRAINS IN THE UNITED STATES. 



in some details. The tendency in recent years has been to consider 

 the biologic forms of our rusts as somewhat closely limited to their 

 host species. Hitchcock and Carleton (58) and Carleton (30) find 

 the stem rust to contain the following forms: 



(a) Pucdnia graminis tritici Erikss. and Henn. on wheat, barley, Koeleria aistata 



(L.) Pers., Festuca gigantea {L.)Y ill., Agropy ron richardsoni Schrad. , Elymus 

 canadensis glaucifolius Muhl., Elymus canadensis L., Hordewn jubahim L., 

 Hordeum murinum L., Dactylis glomerata L., Agrostis alba L., and Agro- 

 pyron tenerum Vasey. 



(b) P. graminis avenae Erikss. and Henn. on oats, several species, Arrhenatherum 



elatius (L.) Beauv., Hordeum murinum L., Ammophila arenaria (L.) Link., 

 Trisetum subspicatum Bean\ . , Dactylis glomerata L., Koeleria cristata (L.) 

 Pers., Alopecurus alpestris, Eolcus mollis, Agrostis scabra^N\\\<i., Polypogon 

 monspeliensis (L.) Desf., Festuca sp. indet., Phleum asperum Vill., Bromus 

 ciliatus L., and Eatonia obtusata (Michx.) Gray. 

 Pucdnia graminis secalis Erikss. and Henn. was not mentioned. 



Eriksson (41, p. 70; 40, p. 294; 42, p. 500; 46, p. 198; 44 and 47) 



finds them as follows: 



(a) P. graminis tritici Erikss. and Henn. on wheat, sparingly on barley and rye. 



(b) P. graminis avenae Erikss. and Henn. on oats, Arena sterilis L., Avena brevis 



Roth., Arrhenatherum elatius Mert. and Koch., Dactylis glomerata L., Alope- 

 curus pratensis L., Milium- efftmim L., LamarcJcia aurea Mch., Bromus 

 arvensis L., Trisetum distichophyllum Beauv., Bromus brachystachys Horn., 

 Bromus madntensisL., Koeleria setacea DC, Festuca myurus Ehrh., Festuca 

 tenuijlora Sibth., Festuca scinroides Roth., Phalaris canariensis L., Phleum 

 asperum Vill., and Briza maxima L. 



(c) P. (iraminis secalis Erikss. and Henn. on rye, barley, Hordeum jubatum L., 



Hordeum comosum J. and Presl., Bromus secalinus L., Elymus sihiricus L., 



Elymus arenarius L., Agropyron repens Beauv., Agropxjron caninum R. and 



Sch., and Agropyron desertorum Fisch. 



The differences in results obtained by these European and American 



investigators have led the writers to examine further into tlie possi- 



bihty of breaking down the barriers between the so-called biologic 



forms. This object, as will be seen below, has been accomphshed 



without much difficulty, and at the same time considerable light has 



been shed on the true nature of the ])arasitism of cereal rusts. 



Experiments on Bioi>o(;ic Forms, 

 description of methods. 



Rusts were collected in Minnesota and were triuisferred to their 

 own host ])lants by artificial inoculations in the greenhouses at 

 Washington, D. C. These constituted the stock rusts. In all the 

 experiments the uredo stage was the spore form used. The cereal 

 host plants were raised in small pots, about 10 plants to a pot, and 

 inoculated in the seedhng stage, either on the first or on the second 

 leaf. The spores were placed on the leaf dry, or they were slightly 

 moistened to enable them to adhere to the leaf surface. The i)lants 

 were then sprayed with water by means of an atomizer until the leaf 



21G 



