258 DISEASES OF FIELD & GARDEN CROPS. [CH. 



on both sides from within outwards, and as the spores in- 

 crease in number they tear the epidermis of the invaded 

 part to shreds, which shreds are, with the spores, speedily 

 carried away by the wind. The pustules illustrated at 

 Fig. 119 may be compared with the sori of a similar 

 nature belonging to Puccinia Bubigo-vera, B.C., Fig. 67, 

 and Puccinia graminus, Pers., Fig. 78. The spores are 

 brownish-black in colour, roundish, and extremely small, 

 as illustrated, enlarged 400 diameters, at Fig. 120. If the 



spores of bunt are now re- 

 ferred to, as illustrated to the 

 same scale at Fig. 1 1 5, it will 

 be seen how different they 

 are in size. The spores of 

 the smut fungus are so ex- 

 X-4OO ' tremely small that it would 



FIO. 120. Spores of the Smut fun- take nearly 25,000,000 of 



gus, Ustilago carto, Tul. Enlarged t ^ em fa cover a superficial 

 400 diameters. . , ml _ -, 



square inch. They are also 



quite smooth, wliilst the spores of the bunt fungus are 

 reticulated and spinulose. Dr. Oscar Brefeld, in his work, 

 Botanische Untersuchungen ilber Hefenpilze Fortsetzung der 

 tSchimmelpilze, Part V., states that some kinds of yeast are 

 nothing more than conidial or larval forms of smut 

 fungi. The reproduction of smut in the yeast condition 

 continues for an indefinite period, so long as the spores 

 are kept upon a suitable nutrient matrix. Upon this 

 nutrient matrix they always remain in the yeast, conidial, 

 or larval condition. If these views are correct they indicate 

 that smut fungi are only truly parasitic during the perfect 

 condition of their existence, and when in the yeast condi- 

 tion lead a non-parasitic life. 



In Fig. 121 the spores of Ustilago carbo, Tul., are shown 

 in different stages of germination enlarged 1000 dia- 

 meters. The extreme smallness of these spores is very 

 marked when compared with the large spores of Peronospora 

 tSchleideniana, Ung., Fig. 15,0; Puccinia graminis, Pers., 



