THALLOPHYTES : FUNGI 



281 



wall, and forms what is called the " black rust," which ap- 

 pears late in the summer on wheat stubble. These spores 

 are the resting spores, which last through the winter and 

 germinate in the following spring. They are called teleuto- 

 spores, meaning the " last spores " of the growing season. 

 They are also called " winter spores," to distinguish them 

 from the uredospores or " summer spores." At first tliis 

 teleutospore-bearing mycelium was not recognized to be 

 identical with the uredospore-bearing mycelium, and it was 

 called Puccinia. This name is now 

 retained for the whole polymorphous 

 plant, and wheat rust is Puccinia 

 graminis. This mycelium on the 

 wheat, with its summer spores and 

 winter spores, is but one stage in 

 the life history of wheat rust. 



In the spring the teleutospore 

 germinates, each cell developing a 

 small few-celled filament (Fig. 252). 

 From each cell of the filament a 

 little branch arises which develops 

 at its tip a small spore, called a spo- 

 ridhim, which means " spore-like." 

 This little filament, which is not a 

 parasite, and which bears sporidia, 

 is a second phase of the wheat rust, 

 really the first phase of the growing 

 season. 



The sporidia are scattered, fall 

 upon barberry leaves, germinate, and 

 develop a mycelium which spreads 



through the leaf. This mycelium produces sporophores 

 which emerge on the under surface of the leaf in the 

 form of chains of reddish-yellow conidia (Fig. 253). These 

 chains of conidia are closely packed in cup-like receptacles, 

 and these reddish-yellow cup-like masses are often called 



Fig. 252. Wheat rust, show- 

 ing a teleutospore germina- 

 ting and forming a short fil- 

 ament, from four of whose 

 cells a spore branch arises, 

 the lowest one bearing at 

 its tip a sporidium.— After 

 H. Marshall Ward. 



