242 



DISEASES OF CULTIVATED PLANTS 



leaves, and more especially the sheathing portions, are seen 

 to be more or less covered with rounded or elongated 

 patches, covered with a delicate greyish-white mycelium, and 

 bordered with brown. These patches often spread entirely 

 over the sheath. When the fungus has reached this stage of 

 development, the lower leaves are dead and the entire plant 



FIG. 69. itGibellinacerealison wheat plant, nat. size; 2,ascus 

 with spores of same, highly mag ; 3, Ophiobolus graminis, on 

 wheat plant, nat. size ; 4, perithecium of same, mag ; 5, 

 spores of same, highly mag. 



dying, so that the ear does not escape from the sheath, or at 

 best is but imperfectly developed. At this stage numerous 

 perithecia are developed on the leaves, leaf-sheaths, and 

 internodes of the stem on those portions previously occupied 

 by the greyish mycelium, but are usually most abundant, and 

 often confined to the inner surface of the leaf-sheaths. 



Perithecia globose, sunk in the tissue of the host, neck pro- 



