324 THE RUSTS OF NOVA SCOTIA. FRASER. 



and, as far as known, aecia are never produced, yet it is very 

 common. 



The heteroecism of rusts was first suspected and established 

 in the wheat rust, P. graminis. For years before botanists 

 made the discovery, practical farmers suspected that the bar- 

 berry was connected with the spread of wheat rust. In 1760 

 a law was passed in the State of Massachusetts for the destruc- 

 tion of barberry bushes. In 1816 Schoeler, a Danish school- 

 master, planted small barberry bushes in the middle of a field 

 of rye and found that the rye around those bushes became 

 rusted while not a rust spot could be found in the rest of the 

 field. He also carried rusted barberry leaves into a field of 

 rye, and rubbed them on the rye plants till he could see the 

 "yellow dust" of the barberry leaves adhering to the plants. 

 These plants were marked and were found to be the only ones 

 in the whole field which became infected with rust. But 

 botanists took no notice of these experiments or of farmers' 

 observations, as they believed the barberry fungus and the rust 

 on rye belonged to different genera. Tulasne showed that 

 the uredinia and telia, which up to this time had been regarded 

 as different genera, were connected. In 1861 -De Bary 

 pointed out that many of the rusts had urediniospores and 

 teliospores and also that the latter gave rise to aeciospores. and 

 conversely the aeciospores to urediniospores. In 1864 he sowed 

 the teliospores of Puccinia graminis on barberry and produced 

 aecia, and in 1865 he sowed aeciospores on rye and produced 

 uredinia and telia, thus establishing the connection of the 

 different forms. However, it was not till about 1880 that the 

 heteroecism of the rusts was generally accepted. Since that 

 time many botanists have carried on infection experiments, so 

 that the number of heteroecious rusts now known amounts to 

 over 150 species. 



Much has been learned of the heteroecious rusts by infec- 

 tion experiments carried on by European and American 

 botanists. In America Farlow and Thaxter for eleven years 



