GRASSES OF IOWA. 



197 



Fig. 87 A., nat-tail 

 fungus {Epichloe 

 typhiiia) on timo- 

 thy. (King) 



Poa, Elymus and Dactylis. The fungus produces 

 a whitish stroma, which surrounds the grass culm 

 near the upper leaf sheaths This velvety ring 

 consists of a loosely arranged mycelium which 

 takes the nourishment from the grass plant, caus- 

 ing the parts above the ring to die, since it pre- 

 vents the conductingof food to the leaves above. 

 This stroma produces small, one-celled conidia 

 borne on conidiophores. As the stroma becomes 

 yellow, deep-seated perithecia occur. These con- 

 tain the asci in which eight hyaline asccspores 

 are found. The fungus spreads from a center of 

 infection to neighboring stalks, especially by means 

 of the conidia. To prevent the fungus from 

 spreading it is advisable to cut the grass at the 

 time the fungus appears on the young plants. 



HYPOCRELLA (HYPOXYLON (PK. SACC.) 



This fungus is closely related to the preced- 

 ing. It produces a thin grayish stroma which 

 usually becomes black and extends along the upper surface of 

 the leaf or surrounds the culm. The perithecia are small 

 and crowded; the asci narrow and linear; the ascospores linear, 

 colorless, with numerous nuclei.* 



The fungus attacks living grass, stems and leaves. 



POWDERY MILDEW OF GRASSES. 



The powdery mildew {Erysiphe graminis D. C.) is a serjous 

 fungus disease at times. It was described by DeCandollef and 

 has been noted by several writers. X 



Every one who has had occasion to walk through a blue 

 grass meadow after a rain, especially in damp and shaded 

 places close to the ground, must have noticed a white mealy 

 covering on the blades of many of the leaves. The Germans 

 have called this mehlthau (literally translated meal dew) which 



*Saccardo Syll. Fung. 2: 581. 



Ellis and Everhart. N. A.m. Pyrenenycetes. 91. 



Peclr. Rep. Mus. State Nat. Hist. 27: 108. 

 +FI. Franc. 6: 106. For synonymy see Loverdo Les Maladies Crypt. 212. 

 J^orauer, Pflanzenkrankheiten. 331. 



Frank. Krankhelten d. Pflanzen. 554. (Ed. 1.) 364. /. 51. (Ed. 2.) 



Tubeuf. Pflanzenkrankheiten. 194. 



Trelease in. Beal. Grasses of N. Am. 1 ; 423. 



Pammel. Fungus diseases of Iowa Forage Plants. 14-15. 



