236 



LIFE HISTORY OF A RUST 



distributed by the wind and germinate at once (Fig. i6i, A) 

 on other wheat plants which soon show the rusty brown streaks 

 of urediniospores. In this way, the pest spreads with great rap- 

 idity from a single center of infection. This formation of ure- 

 diniospores goes on during the summer, sapping the vitaHty of 

 the plant and, in severe cases of infection, materially interferes 

 with the maturing of the grain. 



Fig. i6o. 



Fig. i6i. 



Fig. i6o. The summer and fall stages of a rust, Puccinia: A, rust blotches 

 on leaf of wheat. B, portion of leaf magnified, showing rupturing of the 

 epidermis due to the formation of spores. C, urediniospores or the summer 

 spores which effect a rapid distribution of the parasite during the summer. 

 D, teliospores or fall spores which are dormant during the winter. 



Fig. i6i. Germination of uredinio- and telio-spores: A, the thin-walled 

 urediniospore sending out hyphae from thin places in its wall. This is ef- 

 fected as soon as it is carried by the wind to a moist leaf. B, teliospore ger- 

 minating in the spring and forming a short hypha, from the end of which four 

 cells have been cut off that are forming the basidiospores, b. 



Later in the season, this same mycelium forms in the leaves 

 of the wheat quite a different type of spore. They are formed in 

 the same manner as the urediniospores but are provided with 



