318 



PRACTICAL COURSE IN BOTANY 



stage in the life cycle of the plant, and to this stage the old 

 name uredo is applied, the spores being called uredo-spores. 



360. Black rust. - - Teleuto stage. Next examine with a 

 lens a part of the plant attacked by black rust. Do you 



observe any 

 difference ex- 

 cept in the 

 color? Do the 

 two kinds of 

 rust attack all 

 parts of the 

 plant equally? 



FIG. 452. Uredo spores of wheat rust (Puccinia graminis), T ? , > 



magnified. (From COULTER'S " Plant Structures.") n O t, W n a t 



part does each 



seem to affect more particularly? At what season does the 

 black rust appear most abundantly ? Place a section of the 

 diseased part under the microscope and notice that the dif- 

 ference in color is due to a preponderance of long, two- 

 celled bodies with very thick, black walls (Fig. 453). These 

 are called teleu- 

 tospores, a word 

 meaning " final 

 spores," be- 

 cause they are 

 formed only 

 toward the end 

 of the season. 

 They are de- 

 veloped from 

 the same my- 

 celium with the 

 uredospores, 

 and are not a 

 product of the latter, but collateral with them and belong to 

 the same stage in the life history of the fungus. After they 

 appear, the uredospores cease to be developed at all, and 



FIG. 453. Teleutospores of wheat rust, magnified. 

 (From COULTER'S "Plant Structures.") 



