140 SCIENCE PROGRESS 



smut spores apparently responsible for the disease refused to 

 germinate, or germinated poorly in water. This line of thought 

 led to the next important discovery, based on Brefeld's experi- 

 ments, that when smut spores are placed not in pure water, but 

 in a nutritive solution or on a nutritive medium, they germinate 

 readily and abundantly, producing enormous numbers of conidia 

 which bud and rebud in a yeast-like manner, as the illustra- 

 tions in Brefeld's most valuable Botanische U titer suchungen iiber 

 Schimmelpilze (v., xi., xii.) abundantly show. Brefeld saw at 

 once the great practical importance of his discovery, and an 

 explanation of the oft-repeated remark of farmers that farmyard 

 manure had something to do with the spread of the smut disease. 

 Brefeld's nutritive culture medium of the laboratory corresponded 

 to the organic matter of the manure, and the generations of 

 conidia to similar bodies in the manured soil. Further, smut 

 spores retain their vitality or viable power several years. If, 

 in the rotation of crops, a corn crop followed too closely a 

 smutty corn crop, the latter would have left spores in the soil 

 which the manure would feed in preparation for the later corn 

 seedlings. 



It will occur to the reader that there may be many other 

 sources of contamination of the soil. Brefeld next satisfied 

 himself that the smut spores do not attack the host plant 

 directly, but that the conidia arising from them do. These 

 make their entrance into a host through its soft surface tissues, 

 by means of branching penetrating hyphae. This attack, to be 

 effective, must be delivered before the first blade of the corn- 

 plant is more than half an inch long. The story now seemed 

 complete as regards the aetiology of the smut-fungus. Corn 

 smut is caused by a parasitic fungus, the spores of which need, 

 for vigorous development, to live saprophytically in an organic 

 nutritive medium which causes abundant production of conidia. 

 These, on coming in contact with the delicate surface tissue ol 

 the host, send through it their branching hyphae, and so the 

 host becomes diseased, though the fact is not revealed until 

 harvest time. 



I do not think we know much more now than in 1750 as to 

 the predisposing causes of smut. Practically, all the explana- 

 tions offered have been proved not to hold in one case or 

 another. As in the case of rust, valuable work has been 

 carried on with the object of producing races of corn plants 



