562 



SPECIAL PLANT PATHOLOGY 



host plants or plants. According to Eriksson, six forms can be dis- 

 tinguished in Sweden, namely, tritici (on wheat seldom on rye, barley 

 and oat), secalis (on rye, barley and couch grass), avencs on oat, orchard 

 grass, etc.), pocB (on the blue grasses) , oir« or species of Aira and Agrostis 

 on Agrostis canina and A. stolonifera. 



Fig. 205. — Heads of wheat showing smut (Ustilago tritici), and to the right, 

 appearance of smutted stalks at harvest time. {After Jackson, F. S., Bull. 83, Del. 

 Coll. Agric. Exper. Slat., December, 1900.) 



Stinking-smut {TiUetia fa'tcns (B. & C.) Schrt.). — This is the com- 

 monest smut on wheat in the United States. It occurs in the 

 wheat-growing regions of Canada^ and the Northwest, where it 



1 Gussow, H. F.: Smut Diseases of Cultivated Plants. Bui. 73, Division of 

 Botany, Central Experimental Farm, Ottawa, Canada, March, 19 13. 



