15 



METHODS OF BLOSSOM INFECTION. 



In order to carry out the experimental infection, it was necessary to work out methods 

 approaching most nearly the natural dissemination of the spores. That is, so to imitate the 

 phenomena of nature, that the easily scattered smut spores from the spore masses penetrate with 

 the greatest possible sureness into the blossom of the grain without, however, causing any pos- 

 sible disturbances. For this it was necessary to observe especially that the exact period was reached 

 in which the blossom of the grain to be infected was most widely open, thus furnishing the pre- 

 liminary conditions most favorable for blowing the smut spores into them. Blossom infection 

 naturally could be carried through only in dry weather, best of all in sunny weather, when the 

 host plants are dry and the spores of the loose smut may be easily disseminated. After various 

 experimentation an atomizer of strong rubber and of suitable size was used for this. The smut- 

 ted inflorescences were put in it and the opening closed with a connection which ended in a tube 

 with a corresponding opening. Previous tests had shown that by this means the smut spores 

 can be driven from the atomizer in sufficient amount, most finely distributed and comparatively 

 powerfully.. The heads or panicles to be infected were then placed in a cylinder, the under 

 opening of which was loosely closed with a wad of cotton, and the spores were forcibly blown 

 into it from the open end. After waiting a little for the spores to settle, the heads were taken 

 again from the cylinder. Supplementary tests of heads thus infected proved that in this kind of 

 infection the smut spores were actually carried into the bloom, so far as the existing condition 

 of the single blossoms permitted. Naturally, the number of blossoms of a head which are open 

 at the same time and make possible this penetration is more or less restricted, according to 

 circumstances. The blossoms on a head do not bloom simultaneously, they are generally most 

 advanced in the middle, while those to be found at the base and near the top open later. From 

 this it is evident that, in a single infection by thus blowing in the spores, only a corresponding 

 part of the blossoms of the head can be effectually infected. Thus, infection exceeding a certain 

 per cent may not be expected here. Several repetitions of the infection of single heads are not 

 advantageous, since disturbances of the normal development of the blossoms may always be 

 unavoidably introduced by the processes. 



In nature the conditions for dissemination are incomparably more favorable. Smutted 

 plants, standing in grain fields, do not scatter their smut spores only once when there is enough 

 motion in the air, but constantly throughout the whole time in which the blossoms of the sur- 

 rounding heads are opening successively. Thus the probability of infection of neighboring healthy 

 plants increases appreciably in comparison with infection in cylinders as already described. Rain 

 belongs among the chief disturbances possibly occurring during infection in nature, that is wet 

 weather which deprives the loose smut of its natural fate and carries its spores down on to the 

 soil, where they are lost for blossom infection. However, too dry and too warm weather can 

 also be unfavorable for infection, since it hastens very much the development and ripening of 

 the grain. Germination of th^ spores needs also a sufficient amount of moisture. 



