44 



The earlier experiments have not yet brought out the experimental proof that infection 

 of the host plants is truly brought about by saprophytic centres of infection of maize smut spores 

 which are deposited at a distance from the parts of the maize to be infected. The experiments 

 in this line have l^een carried out since and have been added to by annual repetition. On lots of 

 young maize plants which had already pushed 3-5cm out from the sheath, which therefore, as 

 young germinating seedlings, had become completely immune, smut spores were sown in such a 

 way, that, mixed with good humus soil, they were carefully sifted between the experimental 

 plants. Then a thin layer of horse manure was put on top and the surface stirred a long time 

 with a suitable rake until the manure was equally mixed with the soil. In this condition, all 

 the lots were left to themselves and further observed. It was shown in all cases where the soil 

 had l)een sufficiently infected and the content of dampness had been artificially regulated by rain 

 or by sprinkling at short intervals, that even after a few weeks the appearance of smut occurred 

 in the plants and later increased noticeably. All the phenomena of smut reappeared just as they 

 have already been described, in the leaves, in the staminate blossoms, in the axes, in the adven- 

 titious roots and subsequently also in the pistillate flower spikes' The places of infection were 

 now arranged as described above, and separated one pace from each other, at varying distances 

 from the lots of maize plants so that the air conidia formed on the soil had to be carried farther 

 to the maize plants by wind from the prevailing direction. It was shown that even here infec- 

 tion takes i)lace by means of air conidia, but that it decreases gradually with the increasing dis- 

 tance of the centre of infection from the experimental maize plants. Restricted by the given 

 special conditions the experiments could not be carried out at a greater distance than 20 metres. 

 It was possible to affirm, however, in each case that a number of maize plants had been reached 

 l)y the germs of infection carried by the wind and had become smutted. The easy dissemina- 

 tion of the very small air conidia through the air places no limit of infection in nature. Beyond 

 a certain distance, the results become reduced and only isolated instances of disease occur. 

 Certainly the universal distribution of maize smut is chiefly promoted by air conidia, if not 

 entirely by them. If this be true, the overcoming of this smut can be attained only by burning 

 the smutted plants before they have allowed their smut spores to reach the soil ; for its infection 

 proceeds always from the soil and the spores dropped from smutted plants on to it are later the 

 natural centres of infection for the increase of the disease. 



Further, the experiment was not overlooked of collecting and sowing the still healthy 

 grains of maize spikes, which had been attacked by this smut only in the uppermost parts. It 

 was shown, as might have been presupposed, that this grain, sterilized before sowing, brought 

 forth perfectly healthy plants and that in the interior of the grains no vegetative fungus was 

 present. Of course the smut can be carried over in the seed of maize taken from smutted fields, 

 by the spores which cling to the outer surface. These spores get into the soil and, if it is 

 impossible for them to attack the young maize plants they may still become centres of infec- 

 tion which can bring about a renewed infection from the soil by saprophytic nutrition and by 



(1) See plates III-V, Part XI. 



