2io PROTOBASIDIOMYCETES [CH. 



nor nuclear fusion takes place at any stage, the diplophase being wholly 

 omitted. 



Heteroecism. In many rusts the gametophytic and sporophytic mycelia 

 occur on different host plants. Such forms are termed heteroecious in 

 contrast to the autoecious species where the whole life-history is passed 

 on a single host. It is not surprising that the different spore forms on such 

 species were recognized and described some time before it was understood 

 that they are stages in the life-history of a single fungus. The final proof 

 of the relationship of the aecidia and spermogonia on the one hand and the 

 uredo- and teleutosori on the other, was given by de Bary in 1865 for 

 Puccinia Gmminis, the wheat rust or, as the teleutospore stage was called 

 by early investigators, the wheat mildew. In this plant the haplophase occurs 

 on the leaves of the Barberry (Berberis vulgaris) and the diplophase on 

 wheat, oats, rye and other grasses. 



Long, however, before this relationship was demonstrated, and even 

 before the fungal nature of the disease was known, farmers had begun to 

 suspect some malign connection between barberry bushes and their wheat 

 crop, and had observed that dark areas of blackened and injured wheat 

 were apt to occur in the neighbourhood of such plants. In the State of 

 Massachusetts an act was passed requiring the inhabitants to extirpate all 

 barberry bushes before a given date in 1760 and Marshall, of Norfolk, 

 writing in 1781, says that "it has long been considered as one of the first 

 of vulgar errors among husbandmen that the barberry plant has a pernicious 

 quality (or rather a mysterious power) of blighting wheat which grows near 

 it 1 ." It is hardly to be wondered at that learned persons of the time 

 repudiated this belief, or, as Marshall says of himself, "very fashionably 

 laughed at it." It was not till 1797 that Persoon identified the wheat disease 

 as a fungus and gave it the name it still bears. In 1805 Sir Joseph Banks 

 called attention to its resemblance to the rust on the barberry, suggesting 

 that it might be one and the same species, "and the seed transferred from 

 the barberry to the corn." 



In 1816 Schoeler, a Danish schoolmaster, set himself to deal with the 

 matter experimentally, and applied rusted barberry leaves to some marked 

 plants of rye ; after a few days these were badly affected while not one 

 rusty plant could be found elsewhere in the field. His discovery was con- 

 firmed by the investigations of de Bary, who performed the infection in both 

 directions and under more critical conditions, and it has since been shown 

 that a large proportion of the rusts are in fact heteroecious. 



It seems pretty evident that the autoecious condition must have been 

 primitive and it would be of interest to know what factors determined the 

 adoption of different hosts for the different phases of the life-history. 



1 Rural Economy of Norfolk, 2nd ed. vol. ii, p. 19, London, 1795. 



