202 GRASSES OF IOWA. 



sometimes nearly encircles the stem. The lower leaves are 

 dead. The mycelium consists of thick, branched, hyaline sep- 

 tate threads, which spread over the surface of the host, send- 

 ing haustoria into the cells. The erect threads bear oval or 

 ellipsoidal spores after the fashion of an Oidium. These spores 

 propagate the fungus during the summer. Later immersed 

 perithecia are formed, arising from a deep, white stroma. The 

 perithecia consists of somewhat flattened cells. In the interior 

 occur numerous paraphyses and asci. The club-shaped asci 

 contain eight two-celled yellowish-brown ascospores arranged 

 in two rows. The fungus apparently enters the plant through 

 the delicate tissues of the germinating seedling. 



BL,ACK SPOT DISEASE OF GRASSES. 



The Phyllachm-a graminis (Pers.) Fuckel occurs on many 

 cultivated and wild grasses; other species occur on clover and 

 other leguminous plants. This parasitic fungus disease cause 

 blackish spots on the lower or both surfaces of the leaf. The 

 fungus causing these black spots on grasses has been called 

 the black spot disease of grass. This was first described by 

 Persoon* as Sphaeria graminis. Fuckelf made the correct com- 

 bination. It is generally so called by mycologists. 



During August, and especially later, the coal black spots 

 along the veins are especially prominent; they are considerably 





Fig. 93. Black spot disease of grass (Phyllachora graminis.) A, showing cross- 

 section of leaf through a black mass; B, an ascus with spores enlarged. (A and B. 

 Frank; a after Trelease.) 



*Syn. 30. Dothldea graminis. (Pers.) Fr. Sys. V. 887. 



tSymb. Myc. 216. Saccardo Syll. Fung. 2; 608. Ellis [and Everhart. N. Am. 

 Pyreno. 699 pi. 40. f. 1-4. 



