28o 



FUNGI 



hours and form new mycelia, from which, in six to ten 

 days, fresh spores arise. Formerly this was thought to 

 complete the life history of the fungus, to 

 which the name of Uredo was given. It is 

 now known, however, that the red rust is 

 merely a stage in the life cycle of the plant, 

 |J| and to this stage the old name uredo is 



applied, and the spores are called uredo- 

 spores. 



536 537 

 536, 537- — Leaf 

 of wheat affected 

 with orange leaf 

 rust, Puccinia, ru- 

 bigo-vera, uredo 

 stage: 536. upper 

 side of leaf; 537, 

 under side. 



1? 



400. Black Rust. — Next examine with 

 your lens a part of the plant attacked by 

 black rust. Do you observe any difference 

 except in the color .? Do the two kinds of 

 rust attack all parts pf the plant equally .^ 

 If not, what part does each seem to affect 

 more particularly .'' At what 

 season does the black rust ap- 

 pear most abundantly .' 



It was formerly supposed that 

 black rust was caused by a 

 different fungus from that pro- 

 ducing red rust, and to it the 

 name Puccinia was given, but 

 it is now known to be only another phase of 

 the same parasite that produces the red rust. 

 The name " Puccinia" is retained as a general 

 designation for all fungi undergoing these two 

 phases, and the particular form of fungus that 

 we are now considering is known in all its stages as Puc- 

 cinia graminis. 



401. Teleutospores. — Toward the end of summer the 

 same mycelium that bore the uredospores begins to 

 develop the dark spore clusters that give to black rust its 

 characteristic color and its name. After this the uredo- 

 spores soon cease to be developed at all, and only the dark 

 ones called teleutospores are produced. These remain on 

 the culms in the stubble iields over winter, ready to begin 



S38. — Stalk 

 with Puccinia 

 graminis, le- 

 leuto stage. 



