RUST OF WHEAT 107 



Smut Fungi (^Ecidiomycetes). The various species have 

 their own peculiar host-plants. Thus, we find rusty- red 

 spots of fungal origin on the undersides of Coltsfoot- 

 leaves. Puccinea suaveolens covers the under-surfaces 

 of Thistle-leaves with its brownish-red spores. The 

 plants attacked by these Fungi. are conspicuous in that 

 they appear sickly and yellow in comparison with their 

 uninfected neighbours. Perhaps the most classical of 

 these parasites is the Rust of Wheat (Puccinea graminis), 

 which thrives on cereals during the summer, and in that 

 season scatters orange spores that infect other plants, 

 and thus spread the disease. Later in the year brown, 

 or almost black, spores are produced. These lay on 

 the ground through winter, and constitute a resting- 

 stage. They are termed " teleutospores " (final spores), 

 because they are developed at the end of the season. 

 The teleutospores germinate in the spring. They pro- 

 duce hyphse, which do not form a true mycelium, but 

 produce special cells, called " sporidia," which are, to 

 all intents and purposes, another kind of spore. Now 

 it is remarkable that the sporidia cannot infect a cereal, 

 or any member of the Grass group. They are destined 

 to fail in their mission if a helpful wind does not drift 

 them on to a particular shrub, the Barberry (Ber- 

 beris vulgaris). The sporidia infect the leaves of this 

 shrub, their mycelia spreading through the tissues and 

 feeding at the expense of their host. Here, again, the 

 passion for reproduction asserts itself. Remarkably 

 pretty little yellow cups are produced from the my- 

 celium, and appear on the under-surface of the attacked 

 leaf (Fig. 35). These cups contain spores, and consti- 

 tute the secidium stage of the Fungus, the spores, for 



