134 DIMORPHISM IN FUNGI. 



Amongst the Urojnyces, three forms of development are now 

 recognised, showing that yEcidiiim^ Uredo, .and Uromyces are but 

 conditions or stages of the same fungus, viz. : i — Hymenium, or 

 yEcidiiim ; 2 — Stylospores, or Uredo ; 3 — Teleutos pores, or Uro- 

 myces. This leads us to the consideration of a most important . 

 subject, viz. — the Rusts and Mildews of Wheat. These are of two 

 kinds, according to time of appearance, viz. — Spring Rust and 

 Mildew, and Summer Rust and Mildew. The rust is termed 

 Uredo and the mildew Fuccinia. 



Spring Rust and Mildew. 



The Spring Rust, Uredo rubigo-vera, appears on grasses and 

 cereals in March and April in the form of very minute, livid, 

 yellow pustules. When examined with a power of twenty-five 

 diameters, it is evident that the fungus within the leaf of the 

 wheat has, in reaching maturity, burst the epidermis, and appears 

 as a fine orange-coloured powder carried away by the slightest 

 breath of air. A section through one of these pustules, magni- 

 fied 200 diameters, shows a mass of yellow ovoid spores filled 

 with dense protoplasm and supported on short stalks springing 

 from the mycelium. These spores escape in inconceivable num- 

 bers and fall on to the leaves, where they germinate, protruding a 

 spawn-thread from both sides, into which the vital material pours 

 from the spore. As the spore gets empty, a septum appears and 

 cuts off the connection ; the germ-tube now enters the stomata of 

 the leaf, and there forms fresh mycelium, from which new Uredo 

 pustules arise, and so on until the whole plant is permeated by 

 the spawn. 



As the autumn approaches, the yellow Uredo spots vanish, and 

 black spots, similar in shape, appear, which are pustules of the 

 mature fungus, Puccinia mbigo-vera. The superficial resemblance 

 seems complete except as to colour, but a section through a 

 pustule, magnified 200 diameters, shows a great difference. The 

 spores are blackish-brown in colour and are compound — i.e., they 

 have a joint, or septum, across the narrowest diameter, and 

 besides the spores there are numerous dark, elongated bodies, said 

 to be paraphyses (perhaps undeveloped spores). These compound 

 spores act as resting spores, for although developed in the autumn 



