316 GENERAL MORPHOLOGY OF PLANTS 



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. 



468. 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 ^Ecidiolum, 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 

 was always more badly rusted on the leeward side of barberry 

 bushes. As early as 1760 laws were passed in Massachusetts 

 requiring barberry bushes to be destroyed. A little later a 

 Swedish schoolmaster, Schoeler (in 1816), carried barberry leaves 

 with the cluster cups into a rye field and rubbed the leaves on to 

 the rye, so that he could see the masses of yellow cluster-cup 

 spores on the rye leaves. These rye plants became badly infected, 

 while the remaining plants around them remained healthy, 

 Finally, in 1864-5, de Bary, a celebrated German botanist, dem- 

 onstrated by experimental studies the connection of the cluster 

 cup on barberry with the uredo and teleutospores on wheat, his 



