257 



marked and destructive pests of the corn (see for instance Troyel 1790, 

 Scheler 33). Fjelstrup made experiments for its prevention; he treated 

 the grain of Hordeum with hme and describes (1817) how the fields 

 in which was sowed treated corn were free from smut while the 

 adjoining fields were very smutted. In 1875 P. Nielsen made experi- 

 ments with Ustilago carbo proving that the spores of Ustilago nuda 

 i&. avenae?) cannot keep their germinating power from one year to 

 another, hence the infection of the germinating plants is excluded 

 (see P. N. 76 b & 77 b ''). 



It was, however, not until J. L. Jensen by a long series of field- 

 experiments discovered the marked biological differences of Ustilago 

 carbo that Rostrup resumed the question as a real scientific discussion 

 finding that distinct morphological differences corresponded with the 

 different biological differences; for this reason he divided the old 

 species into five new ones; later on Wille (93) divided the smut on 

 Avena into two species, and, at the same time as Rostrup (90 b) de- 

 scribed the naked smut on Avena elatior as Ustilago perennans, Ellis 

 and Tracy described the covered smut on the same host calling it 

 Cintractia avenae (Journ. of Mycology 1890, Syll. IX ^''); later on the 

 latter has been described by Appel &. Gassner as Ustilago dura so 

 that we have now altogether 7 species. At the same time as the 

 European mycologists and independent of them Kellermann and 

 Swingle (90) attained the same results. At the same time as Ro- 

 strup, Plowright had become aware of the presence of certain dif- 

 ferences within this species, he writes (89^'): "The exosporium in 

 Ustilago segetum has generally been regarded as smooth, but it is 

 rather to be described as granular." The same question has for the 

 last years been made the subject of discussion by the "Kaiserliche 

 biologische Anstalt" in Berlin (see Appel 07 6^ 11) which has by 

 new experiments proved the accuracy of J. L. Jensen's observations 

 asserting the superiority of his preventives (the hot-water treatment) 

 to those suggested by Brefeld and Kiihn. 



At present Ustilago carbo has been divided into seven different 

 species of which three are covered smuts (Ust. hordei, Kolleri, dura). 

 The colour of their spores is brown, and the exosporium is granular; 

 the four other species (Ust. nuda, avenae, perennis and tritici) are 

 naked smuts, the colour of their spores is black, and the exosporium 

 is smooth. The promycelium of Ustilago nuda and tritici does not 

 produce conidies (see R 90 b fig. 1 6^ 5) and will infect the host- 

 plants while they are already blossoming (Jensen 87 b 6^ 88 a, Ro- 

 strup 90 b ^). Ustilago avenae and the covered species infect the ger- 

 minating plants in the same manner as Tilletia tritici &. levis and 

 Urocystis occulta (see R 02 a ^", Appel 07 6. 11). 



J. Lind: Danish fungi. 17 



