Alternate Hosts 



back edges on the surface of living leaves. These 

 spores germinate, and later on produce spores of a 

 totally different kind, and frequently will not attack 

 the same kind of plant as that upon which they were 

 produced. Thus the spores produced by the fungus 

 Coleosporium Senecionis on the needles of the Scots 

 fir, germinate and attack, not that, but the groundsel 

 or the Cineraria and produce totally different 

 symptoms ; Cronartium ribicolum grows in its cup 

 stage on Pinvs Strobiia, but forms its later spores on 

 the black currant ; Puccinia Pringsheimiana has 

 its early cup stage on the gooseberry, its later on 

 the sedge; Puccinia Pruni Uvea first on the anemones, 

 later on the plum ; and so on. The latest spores 

 formed on these second hosts usually rest, and after 

 their rest produce the cup-forming stage on the 

 first-mentioned host only, but an intermediate form 

 generally occurs produced on the second host which 

 attacks that host only. The best-known instance 

 is probably the red rust of wheat. In spring the 

 fungus, Puccinia graminis, forms whitish cups 

 (aecidia) on the leaves of Barberry. The yellowish 

 spores (aecidiospores) attack the wheat, and the 

 mycehum in summer forms reddish groups of spores 

 (uredospores) in small patches on the wheat leaves. 

 The uredospores germinate immediately and attack 

 other areas on the wheat leaves, so spreading the 

 infection. Towards autumn the myceliimi which 

 has hitherto produced uredospores forms another 



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