RUSTS (UREDINE^E) 247 



by clusters of bicellular spores (Fig. 131, d), again borne singly 

 at the ends of projecting hyphae, and provided with a thick dark 

 brown membrane (Fig. 131, b, t.) which has a thin germinal 

 pore in each cell. 



With the advent of spring both cells of the teleutospore put 

 out a short hypha composed of four cells (Fig. 131, c), each of 

 which gives rise to a short process bearing a small spherical 

 gonidium (basidiospore, ba.). The latter is only capable of further 

 development if carried by the wind to a plant of the Wild 

 Barberry (Berberis vulgaris). In that case a mycelium is pro- 

 duced within the new host, and the presence of the disease is 

 soon manifested by the appearance, usually on the under-surface 

 of the leaf, of groups of small orange-coloured cups (the cluster- 

 cups or cecidia, Fig. 131, a). The minute specks, recognisable 

 on the upper surface of the leaf, are caused by small flask-shaped 

 cavities (spermogonia, Fig. 131, e, s.) containing reproductive 

 cells of unknown function. 



In a vertical section (Fig. 131, e) the hyphse of the aecidium 

 (ae.) are seen to form a compact bounding wall and a dense 

 interwoven mass at the base, whilst occupying the floor of the 

 cup is a palisade-like hymenial layer whose vertical hyphae bud 

 off rows of orange-coloured acidiospores. The latter, if carried 

 by the wind to Wheat or other Grasses, give rise to a new 

 uredo-form. 



Whilst the cells of the ordinary mycelium in the Barberry-leaf 

 are uninucleate, they become binucleate in the young aecidium, 

 and the resulting spores are similarly provided with two nuclei. 

 The binucleate condition persists throughout all the uredo-forms, 

 and the cells of the young teleutospores show the same feature, 

 but fusion of the nuclei occurs as the latter mature. 



The existence of the Fungus on different host-plants, at 

 different stages of its life-cycle, is paralleled among animal para- 

 sites (e.g. Malarial Parasite, Tapeworm), and affords one means for 

 the extermination of the disease, viz. by the eradication of one 

 host. This is, however, only partially successful, since Wheat 

 Rust occasionally appears in successive years, even where the 

 Barberry does not grow (e.g. Australia), which is probably due 

 to the persistence of uredospores through the winter. In some 

 Rusts there is no uredospore phase (e.g. Puccinia anemqnes), 



