i 4 4 SCIENCE PROGRESS 



the stigma and through the stigmatic tissue towards the 

 ovary. When the harvest of inoculated plants was gathered, 

 it was found that both the cylinder-infected and the hand- 

 infected specimens gave grains which seemed quite healthy 

 and normal. They were stored and in the following year 

 sown under strict sterilisation conditions. The result was 

 astonishing, in that in the case of some of the pots of grains 

 from hand-infected flowers every plant showed a smutty 

 flower spike, 1 and in the case of the cylinder-infected plants 

 the resulting grains gave on germination, on an average, as 

 many as 26 per cent, of smutted plants. The evidence was 

 conclusive that wheat plants can be infected in their flowers 

 with air-borne smut spores, and that the resulting infection 

 reveals itself not in the same year, but first in the following 

 season in the smutted ears at harvest time. Microscopic 

 examination showed the abundant presence of smut mycelium 

 in the apparently healthy grains, and this mycelium became 

 more evident in the growing point, etc., as the grains sprouted. 

 Experiments under various forms showed, too, that sprouting 

 wheat seedlings, unlike oat ones, are almost or quite free 

 from attack by smut spores. Thus in wheat the chief cause 

 of smut is the infection of the flowers by air-borne spores. 

 Infection of the wheat seedling is an almost, if not quite, 

 negligible cause. Infection experiments on barley similar to 

 those on wheat were carried out. Barley proved less favourable 

 than wheat, as the flower proper is less exposed and there 

 is more difficulty in consequence in making sure that the 

 smut spores actually reach the stigma or ovary wall without 

 injury being done to the flower in the operation. The flowers, 

 too, in the same spike are not so uniformly and simultaneously 

 open. Still the results of infection are in principle the same. 

 In the case of hand infection of individual flowers total infection 

 resulted in one case, and in cylinder infection as many as 

 20 per cent, of smutted grains were obtained. Infection of 

 barley grain or barley seedlings was unsuccessful. Hence in 

 barley, as in wheat, the chief, if not the only, source of smut 

 infection is the smutty ears in the field. The wind which 

 carries the pollen grains to the stigmas, and thus gives cross 

 and wind pollination, carries also the smut spores from 



1 This is well shown in the illustrations accompanying Brefeld's paper 

 (Bd. xiii. op. tit.). 



