FLOWERLESS PLANTS 



165 



Uredospores and a teleuto- 

 spore (/) of wheat rust. — 

 De Bary, 



spots are caused by collections of spores of the rust. The mycelium of the 

 plant is within the blade of the leaf, where it takes its food supply from the 

 living cells of the green leaf. The mycelium 

 sends up stalks through the stomata of the leaf ; 

 it is these that hold the sporangia, filled with 

 myriads of yellow-brown spores. The spores 

 produced in the summer time are thin-walled 

 and easily blown by the wind; wherever they 

 alight on a wheat plant, there they germinate to 

 form another mass of hyphse within the leaf. 

 These parasites again produce more of the uredo- 

 spores, as the summer spores 



are called. In the early fall 



the rust, instead of forming 



thin-walled spores, produces 



a curious, double, thick- 

 walled spore in its place. 



This spore, known as a te- 



leutospore, remains dormant 



during the winter. In the 



early spring it germinates 



wherever it happens to have 



fallen, as it is not at this stage a true parasite. Upon 



germination it forms a threadlike body. On this body 



are formed tiny sporelike 



structures which have been 



named sporidia. The spo- 



ridia germinate only upon 



the barberry, where they 



form a mycelium within the 



leaf. 



This mycelium soon 



forms little masses of spore 



cases which, because of 

 their appearance, are called cluster cups. The 

 cluster cups may easily be seen with the naked 

 eye on the surface of the infected barberry leaf. 

 Spores from the cluster cups are carried by the 

 wind to a neighboring wheat field, and there 

 germinate upon the blade of wheat, to form the 

 parasite we have already called wheat rust. 

 In some cases the cluster-cup stage appears to 

 be left out of the life cycle, the sporidia germinating directly upon the 

 wheat plants. 



Teleutospore germi- 

 nating and form- 

 ing sporidia, s, s. 

 (From Coulter, 

 Plant Structures.) 



Section through a cluster cup 

 of wheat rust in the leaf of 

 barberry. 



