SMUT OF CORN. 257 



diseased grain at first presents a whitish viscous mass, 

 which is produced at the expense of the tissues and juices 

 of the invaded plant. This viscid mass at length exhibits 

 a structure of closely packed cells filled with a homo- 

 geneous mass of minute granules ; the cell walls ulti- 

 mately disappear, and the whole contents of the invaded 

 organ appear as one black dusty mass of simple smooth 

 spores. The disease is, however, by no means confined to 

 the grain, as it attacks every part of the panicle with its 

 spikelets, including their slender stems, with equal viru- 



X 25 



FIG. 119. 



Fragment of glume of oats, showing burst pustules of the Smut fungus, 

 Ustilago carbo, Tul. Enlarged 25 diameters. 



lence, till at last the glumes and other parts are left as 

 transparent ragged fragments thickly coated with the 

 masses of black spores, which have been produced at the 

 expense of the normal tissues of the spikelet. If a frag- 

 ment of an infected glume is now taken, and enlarged 

 twenty-five diameters, it will be seen as at Fig. 119. 

 This shows (horizontally) four of the fine ridges and 

 three minute furrows, which can be almost seen with 

 the unaided eye on every glume belonging to oats. 

 The fungus bursts through the glumes and other structures 



