286 GENERAL MORPHOLOGY OF PLANTS 



wheat rust can live through the winter in the teleutospore stage. 

 Since the sporidia from the teleutospores cannot infect the cereals 

 or grasses but only the barberry, the appearance of the wheat 

 rust in early spring, in regions where the barberry does not exist, 

 has long been a mystery. It is well known that in southern lat- 

 itudes, as in the Gulf States in America, and along the Mediter- 

 ranean coast in Europe, the wheat rust can live through the win- 

 ter in grains and grasses in the uredo stage, since the climate is 

 so mild. This led to the belief that southern winds in the spring 

 bore the uredospores northward and thus produced sudden and 

 widespread infection in northern latitudes. This probably does 

 occur to a certain extent. But recent investigations in northern 

 Europe, in Wisconsin and North Dakota show that the uredo 

 stage of some of the grain rusts, formed late in the autumn, lives 

 through the winter and the spores germinate in the spring. The 

 few infections from these early in the spring produce centers from 

 which a second widespread and serious infection follows. In 

 places in the northern peninsula of Michigan the ground is cov- 

 ered so deeply with snow that the ground does not freeze in the 

 wheat fields. Fall wheat which has the uredo stage on it can 

 thus carry the disease over the winter. The mycoplasma theory, 

 propounded by the Swedish botanist Eriksson, according to 

 which the protoplasm of the host and fungus is blended during 

 the winter, and in the spring the fungus plasma can withdraw 

 from this mycoplasma blend and form the mycelium, is not gen- 

 erally accepted. 



453. Early history of our knowledge of the wheat rust. 

 This history makes a very interesting chapter of the story of 

 botanical investigations, which is fascinating to read, but a brief 

 account only can be given here. A half a century ago it was 

 supposed that the four forms of the wheat rust described above 

 (^Ecidium, spermogonium or ^cidiolum, Uredo, and the teleuto- 

 stage, or Puccinia) were distinct genera of plants, and that the two 

 former belonged to a distinct family of plants. Prior to this time, 

 the farmers of England, in the early part of the i8th century, 

 believed the barberry plant caused wheat rust, because wheat 



