728 FUNGI 



great numbers of chlamydospores which are shed off from the 

 mycelium of the parasite living within the tissues of the wheat 



leaf. 



The chlamydospores are the 

 summer spores of the fungus and 

 are termed uredospores. They are 

 single cells of oval form {A, Fig. 246). 

 The outer coat of each spore is 

 thick, and when mature is covered 

 with very short fine spines; in it 

 are four thin places or germ-pores, 

 situated at even intervals around its 

 Fig. 246.— a, Uredospore of p«c- smallest circumference. The inner 



czaia^ramims Fers.; i^, uredospore 



germinating. (Enlarged 420 dia wall of the Spore IS thm, and the 



meters. ) 



spore-contents are coloured with 

 drops of a yellow or orange oily substance. 



When placed in water as soon as ripe they germinate in a 

 few hours; germ-tubes make their appearance from one or 

 more of the germ-pores and develop to a considerable length 

 {B, Fig. 246). If the process takes place in a wheat leaf, the 

 hypha grows along the surface for a time and finally enters into 

 the leaf through an open stoma or penetrates directly through 

 the epidermal cells. The hyphal filament develops in the inter- 

 cellular spaces of the soft parenchyma between the veins of the 

 leaf, and a compact septate mycelium is soon produced which is 

 confined to a small localised area within the tissues of the host. 

 Upon the mycelium arises a dense bundle of short vertical 

 hyphae bearing a crop of uredospores ; the latter as they grow 

 burst through the epidermis and form a ' rust ' spot or sorus on 

 the outside of the leaf. 



The mycelium continues to produce uredospores during a 

 period of eight or ten days, and as each spore when carried 

 by the wind or by insects to a wheat plant is capable of 

 producing a new spot of rust, it is readily understood how 



