224 



LIFE HISTORY OF A RUST 



dium sends out a delicate tube into the end of which the cell 

 contents passes, thus forming a small spore, known as the basidio- 

 spore. This basidial stage completes the life history of the fun- 



FIG. 160. 



FIG. 161. 



FIG. 160. 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, uredospores or the 

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

 summer. D, teleutospores or' fall spores which are dormant during the 

 winter. 



FIG. 161. Germination of uredo- and teleutospores: A, the thin-walled 

 uredospore 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, teleutospore 

 germinating in the soring and forming a short hypha, from the end of 

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



gus for the basidiospores are carried to the leaves of the barberry 

 and begin again the life cycle of the parasite by forming the 

 cluster cups. 



It is not surprising that this story was not unravelled for a 

 long time and that these different stages of the parasite were 

 known as distinct species. The first clue to the relationship was 



