CORN SMUTS AND THEIR PROPAGATION 141 



which would prove immune to smut. Another line of investiga- 

 tion has been also followed with considerable success. Various 

 fungicides have been utilised. They all depend for their success 

 on their power to kill the adhering smut spores without injuring 

 the grain. I carried out in 1900, for the Congested Districts 

 Board, a number of experiments with various fungicides of 

 proved value. 



Hot water, potassium sulphide, "sar" (essentially sodium 

 sulphide), copper sulphate, and formalin were all tried with 

 success. Smutted oats soaked in water at a temperature of 

 132 F. for five minutes are not injured appreciably in their 

 sprouting power, but the smut spores clinging to the grain are 

 killed. Formalin (0*2 per cent, solution), used for two hours, 

 has a similar action. Though every precaution was taken in 

 these experiments, and the time, trouble, and expense were fully 

 justified by the results, yet the crops were not entirely free from 

 smut. In the west of Ireland this result was easily explicable. 

 In many cases potatoes and oats alternate year after year, and 

 I felt I might be putting treated seed into a smutty bed. In 

 other cases such a solution is not available. What, then, is the 

 explanation here? Is the grain harbouring within itself some 

 stage in the smut fungus which is not killed by the surface action 

 of the various fungicides ? 



This same persistence of disease beyond the known explana- 

 tions available has troubled rust investigators also. Ericksson, 

 who has done so much both in the investigation of the rust 

 diseases, and in the attempt to produce races of corn immune 

 to rust attack, has proposed an explanation in his well-known 

 Mycoplasm theory. 



According to this theory the rust fungus exists in the corn 

 plant in a dormant state — in a plasmodium-like form — in the 

 protoplasm of the host cell, and takes on the definite mycelial 

 (thread-like) form when the (unknown) conditions become 

 favourable to its further development. If the conditions are not 

 favourable, it remains in its dormant condition ; the corn plants 

 grow to maturity and appear to be free from rust. I cannot 

 help comparing the various arguments and explanations by 

 which this theory is supported with the successive explanations 

 offered in the case of fertilisation in flowering plants thirty or 

 forty years ago. 



The rust and smut fungi are so closely allied that one would 



