THALLOPIIYTES: FUNGI 



281 



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

 pears late in the summer on wheat stubble. These spores 

 are the resting spores, Avhich last through the winter and 

 germinate in the following spring. They are called Icleuto- 

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

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

 from the urcdospores or " summer spores." At first this 

 teleutospore-bearing mycelium was not recognized to bo 

 identical with tlie uredospore-bearing mycelium, and it was 

 called Purciniu. This name is now 

 retained for the whole polymorjjhous 

 plant, and wheat rust is I'ucclnia 

 grmninis. This mycelium on the 

 wheat, with its summer sjDores and 

 winter spores, is but one stage in 

 the life history of wheat rust. 



In the spring the teleutospore 

 germinates, each coll 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 s2io- 

 ridiimi, 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 tlie first phase of the growing 

 season. 



The sporidia are scattered, fall 

 ujion barbeiTy leaves, germinate, and 

 develop a mycelium which spreads 

 through the leaf. This mycelium produces sporophores 

 whicli 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 



Hi. '.'53. Wheat rnst, show- 

 ing;: a teleutospore germina- 

 ting and forming a short fil- 

 ament, from fonr of whose 

 cells a spore branch arises, 

 the lowest one bearing at 

 its tip a sporidinm.— After 

 H. Marshall Ward. 



