RUST FUNGI— UREDINEAE 245 



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latter. In the one remaining genus of the section, that of 

 Cronartium, the teleutospores surround a vertical columella, 

 but in external appearance the species resemble Uredines 

 as little as possible, and are not unlike persistent tendrils of 

 some member of the Melanconieae. 



The Didymosporae are well typified by the large and 

 important genus Pioccinia, with its transversely septate teleuto- 

 spores. The grades are like those of Uromyces, viz. spermo- 

 gonia, aecidia, uredospores, and teleutospores ; but a different 

 element comes into the subsidiary grouping, since it is con- 

 tended that in some cases these grades are not all passed upon 

 the same host. It is perfectly true that in one typical group, 



Fig. 116. — Section of aecidia and spermogonia. S.P.C.K. 



that of the Auto-jpucciniae, all the grades are developed on the 

 same species of plant ; but in the Hetero-pucciniae, although 

 all the same grades are affirmed to be present, yet the spermo- 

 gonia and aecidia appear on one species of plant, generally a 

 Dicotyledon; whilst the uredospores and teleutospores make their 

 appearance on a plant belonging to quite a distinct genera of 

 plants, mostly a Monocotyledon. Now the doctrine which 

 associates these forms is that designated Heteroecism, and 

 although some writers contend that the facts are not effectually 

 proved, and therefore dispute the conclusions, others accept 

 the inferences derived from artificial cultures as conclusive, 

 and bow down to Heteroecism. Whichever may ultimately 

 succeed in persuading the rest, it is manifest that Heteroecism 

 for the present is the favourite, and consequently the faithful 

 are happy in finding the four grades separated, two on one 

 kind of matrix and two on another. To quote a very familiar 

 example, the spermogonia and aecidia of the berberry are found 



