19 



BLOSSOM INFECTION IN WHEAT. 



We will now turn to the experiments made in the last four years with forms of loose 

 smut, and their detailed results. We will begin with experiments on wheat and the loose smut 

 belonging to it, which Kostrup named Ustilago tritici. Wheat is a plant well suited for blossom 

 infection. The blossoms of the different varieties open differently, but the stamens generally 

 grow free and the openings and cracks formed between the glumes are wide enough to make 

 possible infection by spores. When inoculating the separate blossoms, only very little work is 

 necessary in order to introduce the smut spores into them by means of a brush. Care was always 

 taken that a larger number of spores was introduced into the blossoms in order to insure infec- 

 tion by this means. The stigmarS do not extend far enough out to make possible a limiting of 

 the infection to them alone. Since, however, there are present in the ovary itself \oung tissues 

 in themselves accessible for the germs of infection, it is not very important if the possibility 

 of carrying out the infection separately on the stigma and on the ovaries is very much restricted. 

 After infection has taken place, the single heads on which the blossoms have been infected, the 

 non-infected buds having been removed, were marked with colored, non-fading threads in order 

 to distinguish them and to make certain their harvesting when ripe, later in the autumn. A 

 record was kept of the single forms of infection and in it were entered at the same time minor 

 details, weather and air temperature. On the third or fourth day after infection some of the 

 infected blossoms were investigated in order to determine how the introduced smut spores had 

 behaved. It was possible to observe with certainty that almost all spores had germinated in 

 the stigma secretion, especially on the feather-like stigma itself, and that long threads extended 

 from the germinating spores, which had sprouted out on the stigma tissues, and were lost 

 among them. Difficulties arose in later observations, undertaken to follow still further the pene- 

 tration of the germinating tubes through the stigma, since a clear dififerentiation of the fine 

 threads of the fungus decreased gradually; thereby the growth of the tubes through the stigma 

 into the young ovary could not be seen with certainty. There is, however, nothing against the 

 assumption that the germs of infection, germinating luxuriantly on the stigma, and growing 

 down into it by means of their tubes, reach at last the ovaries themselves. The same may hold 

 good for those spores which germinate directly on the young ovary and penetrate its young 

 tissue. Nothing more than the above given details can be learned by microscopic observation. 

 The ripening of the young grain was watched with great care, and, when ready, it was har- 

 vested just as carefully. The harvested heads were kept in a dry place and hung up in loose 

 bags for later ripening. Judging by external appearances, from all the infected blossoms, only 

 healthy grains were harvested, in no single case of which a trace of smut was found. 



Besides the infection of separate blossoms, cylinder infection was now undertaken in 

 wheat. The heads on which this was carried out were especially marked with colored threads 

 in order to distinguish them in harvesting. After cylinder infection, the microscopic examination 

 of the blossoms for introduced smut spores was not omitted, as well as the ascertaining of their 

 germination on the stigma. 



