290 



USTILAGINEAE. 



shoot. Spores are developed only in the inflorescence, which 

 in consequence fails to reach its full development as a panicle, 

 and remains more or less spike-like and enclosed in a leaf- 

 sheath. The parts of the inflorescence become completely filled 



Fi(!. 160.— Ustilago tritici. Wheat-smut. The central ear is normal and 

 liealthy, the others are smutted and most of the spores ai'e already shed, 

 (v. Tubeuf phot.) 



with a sporogenous mycelium from which arise the spore-masses ; 

 these are at first enclosed in whitish coverings consisting of 

 tissues of the host-plant, but when mature they escape as a black 

 dust or powder. 



