. Les Britanniques rouilles (Uredinales) leur biologie et classification. Les champignons de la rouille. 42 Puccinia graminis. Eigi 25. Puccinia graminis. a, aeoidia sur Berberis ; ft, uredo- spore ; c, teleutospores. tiges ; ces différences pour la partie systématique peut être con- sulted (Fig. 25). Il y a, cependant, un point de différence liée à P. graminis qui possède un grand intérêt biologique-son virtuel dans secidial- dépendance de la scène. Pendant longtemps, il était connu que les buissons d'épine-vinette dans les haies a causé "blanc" sur le maïs dans les champs voisins, et quand, en 1864-5, De Bary

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. The British rust fungi (Uredinales) their biology and classification. Rust fungi. 42 PUCCINIA GRAMINIS. Eigi_25. Puccinia graminis. a, aeoidia on Berberis ; ft, uredo- spore; c, teleutospores. culms; for these differences the systematic part can be con- sulted (Fig. 25). There is, however, one point of difference connected with P. graminis which possesses great biological interest—its virtual in- dependence of the secidial stage. For a long time it had been known that Barberry bushes in the hedges caused "mildew" on the corn in the neighbouring fields, and when, in 1864-5, De Bary proved the heteroecism by experimental cultures, it was too hastily assumed that the secidium on the Berberis vas just as es- sential to the rust on the corn as that on the Nettle is to the rust on the Sedge. Many facts now tend to show that this is not the case. In Australia and the plains of India the Barberry is un- known except as an introduced plant, yet the Puccinia occurs everywhere and does enormous damage. McAlpine records, in his Rusts of Australia that he made numerous attempts to infect imported species of Berberis with the rust of Australian wheat which is morphologically undistinguishable from the P. graminis of Europe, but all his efforts were in vain. The inevitable inference is that P. graminis, as it occurs in those countries, is a " biological" race which maintains itself by other than the primitive means. A similar thing is true, according to Lagerheim, in Ecuador, where also rust flourishes and does great harm. The facts now known concerning the specialisation of the Black Rust are treated of in a separate chapter, but there is one point which must be mentioned here. This concerns the mode by which fresh epidemics are produced each year. Even if the Barberry is present, it is by no means certain that it plays any important part in these annual attacks. Apart from that, there are several possibilities: (1) the fungus may winter. Please note that

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