142 SCIENCE PROGRESS 



expect a hypothesis such as the mycoplasm theory to be applied 

 to the smut question. That this has not occurred is, in part, 

 due to the fact, I think, that it is only quite recently that one 

 has realised that the failures in the attempt to eradicate smut 

 from grain by treatment with fungicides are not due to the 

 imperfection of the method of treatment, or to the presence of 

 smut spores in the soil in which the treated seed is sown. It is 

 well known that the adaptation of the smut fungus to the corn 

 plant is so complete that there is, in the growing corn plant 

 nursing the smut pest, practically nothing to distinguish it from 

 a growing smut-free plant until the corn plant goes into flower 

 and fruit, when the smut reveals itself by its dark colour and 

 destructive action. Is it possible that just as the growing corn 

 plant while actually harbouring the smut is apparently healthy, 

 so the corn grain may in some cases, owing to the difference 

 in the time of attack of the host plant, be also apparently 

 healthy, but yet in reality have in it the mycelium of the smut 

 fungus ? The latest work in the investigation of smut diseases 

 supplies in part an answer to this question. Already in 1895 

 Brefeld had published a further instalment of the results of his 

 smut investigations which gave the key to the next advance. 

 We have seen that the oat plant is infected in its earliest stage 

 of germination, and that the adaptation of the smut fungus to 

 the host is so complete that it is only when the host forms its 

 flowers the smut reveals itself in these flowers and fruit — i.e. at 

 the end of the plant opposite to that at which it enters. 



In the Indian corn {Zea Mais) the smut is not confined 

 to the flowering organs. The smut tubercles or warts found 

 in the " cobs," and sometimes the size of a man's head, may 

 be accompanied by others found in other parts of the plants, 

 e.g. on the adventitious roots at the basal nodes, and even 

 on the styles and stigmas of the flowers. This is not a general 

 outburst of smut galls in a plant due to one attack. Each 

 is a local development produced by a local attack. If adven- 

 titious roots are attacked, the disease is local. Germination 

 of the Zea smut spores gave Brefeld the key. The spores do 

 not germinate in water ; they require a nutritive solution in 

 which to sprout. The conidia in the end form a mycelium 

 on threads of which certain aerial conidia arise. It is these 

 which are the sources of infection : they are carried by the air 

 twenty yards or more, and wherever, in the Indian corn 



