48 



INFECTION OF PANICUM (RISPENHIRSE) AND ITALIAN MILLET. 



Besides the two plants experimented upon, maize and Indian millet, with the corre- 

 sponding forms of smut, during the last ten years two other experimental objects were grown 

 supplementally which are especially well suited for the purpose of infection. They are first 

 Panicum with Ustilago Panici miliacci (U. destruens), and then Italian millet with Ustilago 

 Cramcri (U. Setariae). , 



In Panicum the occurrence of smut is especially characteristic in its external appearance. 

 In the plants attacked, the otherwise loose, long, panicle-like inflorescence is shortened as much as 

 possihle and all the single attacked blossoms united in a smut gall, which is enclosed by sheath 

 leaves. These leaves have undergone a complete fungus pseudomorphosis from mycelial threads 

 which have remained sterile and form a dazzling white envelope about the thick clump of 

 spore masses. The smut galls are sunken within the unchanged green leaves of the upper axis 

 and are only a very little exposed to the open air. The plants attacked, in contrast to a healthy 

 one with its long, outstretched blossom-panicle, make an entirely different im])ression, so that 

 they may be recognized in the field even from a great distance. The black spore masses 

 in the interior of the gall are not disseminated. They are, however, easily germinated in nutrient 

 solution or in water and produce four-celled hemibasidia, in which a formation of conidia 

 occurs, sometimes to a lesser, sometimes to a greater amounts The conidia very rapidly 

 grow out to germ tubes and form in dilute nutrient solutions small mycelia, on the threads of 

 which may be observed the formation of air conidia. Further particulars are to be found dis- 

 cussed in detail in Part V of this work. 



The ripened smut spores, sieved and well-preserved throughout the winter, are purified on 

 a centrifugal sieve and result, after twenty-four hours' retention in dilute nutrient solution and 

 also in water, in a directly aggressive material for infection. One can follow the rapidity with 

 which the spores germinate and form hemibasidia with conidia, which in turn grow out to germ 

 tubes. Inoculation was undertaken on previously chosen grains of Panicum. in which germi- 

 nation had just started, by means of the atomizer and the cultures, protected from the light, 

 were set back in a moderately warm place. After the lapse of a few weeks, the cultures were 

 opened, at first still protected, in order that they might be planted. In infected plants in a series 

 of experiments extending over several years, an average of 60-70% of smutted plants was har- 

 vested. The result in healthy plants could be explained easily by the fact that the compara- 

 tively small germinating seedlings of Panicum ofifer only a limited surface for the spraying on 

 of the germs of infection. However, the discoveries obtained previously with Indian millet 

 were established here also, in obtaining a percentage of smutted plants by delayed development 

 of the host plants, that is, of the young germinating seedlings. Seed from former years was 

 used for the experiments and it was determined with certainty that a slower germination took 

 place here, in which infection was carried out by means of the atomizer in the way described. 



(1) See illustrations on plate VII, Part V. 



