THE WHEAT RUST 73 



variously called " blight," " mildew," or " rust." In 1864, De Bary 

 proved that the rust on the barberry and that on the wheat are differ- 

 ent stages in the Hfe history of a single ftingus. This was the first 

 case in which two hosts were shown to be necessary to complete the 

 life history' of a fungous parasite. De Bary's results were announced 

 in Januarj', 1865. In June of the same year. Oersted showed the 

 connection between the rust on red cedars and that on pear trees. 

 Since De Bar>-'s discovery, the planting of barberries in grain-raising 

 regions has been forbidden by law in England and other European 

 countries, as well as in some American states. Meyen suggested in 

 1 84 1 that the structures in which the spermatia and the spring spores 

 are borne are respecti\-ely male and female organs. This notion re- 

 ceived much support. But in 1904, Blackman and Christman dis- 

 covered the cell unions that occur at the base of the cluster cups, and 

 so showed that the spermatia do not now act as male cells, whatever 

 may have been the case in the past. Beginning with De Bary and 

 his contemporaries, a great amotint of study has been devoted to rusts. 

 Up to ISSS, 1225 species of rusts had been described, of which 455 

 belonged to Puccinia, the genus to which the wheat rust belongs. 

 In 1897, about 1700 rusts were known, of which over 700 were species 

 of Puccinia ; and in 1 904, the number of species of Puccinia alone 

 had risen to 1226 — as many as the total number of rusts known 

 sixteen years before. 



