I 



ORDER UREDINALES (tHE RUSTS) 395 



rust of the sunflower {Helianthus annuus L. and other species) has its 

 sporidial infection on the sunflower with the production of a monocaryon 

 mycehum which produces the spermogonia and the aecial primordia. In- 

 fection by aeciospores produces in the same host species or even in the 

 same plant the dicaryon mycelium from which arise the urediospores and 

 teliospores. It may happen that both types of infection may occur on the 

 same leaf. 



Of the rusts of more or less economic importance the hosts are indi- 

 cated below for the different stages of a few species, showing that 

 both heteroecious and autoecious rusts may be enemies of cultivated 

 plants. The list contains only a very few of the many rusts that attack 

 important crop plants. The customary symbols are used, viz., 0, spermo- 

 gonial development, I, aecial stage, II, uredial stage and III, telial stage. 



Heteroecious Species 



Puccinia graminis Pers., Black stem rust of small grains: and I on Berberis vul- 

 garis L., barberry; II and III on small grains (wheat, rye, barley, oats) and 

 various other grasses. 



P. rubigo-vera tritici (Erikss. & Henn.) Carl., leaf rust of wheat: and I on species 

 of Thalictrum; II and III on wheat (Triticuni). 



P. coronata Corda, crown rust of oats: and I on various species of Rhamnus; II 

 and III on oats (Avena sativa L.). 



P. sorghi Schw.: and I on Oxalis strida L.; II and III on maize (Zea mays L.). 



Gymnosporangium juniperi-virginianae Schw. : and I on apple {Malus sylvestris 

 Mill.); Ill on red cedar (Juniperus virginiana L.). 



Uromyces dianthi Niessl. {U. caryophyllinus Wint.): and I on Tithymalus sp.; 

 II and III on carnation (Dianthus caryophyllus L.). 



Cronartium ribicola Fischer, white pine blister rust ; and I on white pine (Pinus 

 strobus L.) ; II and III on various species of currant (Ribes) and gooseberry 

 (Grossularia) . 



Uredinopsis spp.: and I on species of fir (Abies); II and III on various ferns. 



Autoecious Species 



Gymnoconia peckiana (Howe) Trotter: 0, I, and III on blackberry, dewberry, 



and black raspberry (Rubus spp.). 

 Uromyces phaseoli typica Arth. : 0, I, II, and III on American beans (Phaseolus 



vulgaris L.). 

 Puccinia asparagi DC: 0, I, II, and III on asparagus (Asparagus officinalis L.). 

 P. helianthi Schw. : 0, I, II, and III on sunflower (Helianthus annuus L. and some 



other species). 

 Phragmidium spp.: 0, I, II, and III on various species of rose (Rosa sp.). 



In the case of heteroecious rusts efficient control can be obtained by 

 the elimination of the alternate host in case the rust is unable to over- 

 winter on the host that is of economic importance. Thus in the northern 

 portions of the United States and of Europe the extermination of the 

 barberry has greatly reduced the ravages of the black stem rust because 

 this rust cannot survive the winter except as teliospores on the over- 



