262 



FOUNDATIONS OF BOTANY 



U 



prepared cross-sections through the sorus are available, especially if 

 the material is fresh. Examine the spores and note the shape, color, 

 and surface. If the spores are shrunken, a drop of potash solution 

 will restore the natural plumpness. Draw. Spore-measurements are 

 important in determining species. The uredospores of Puccinia 

 graminis may be distinguished from those of other species common 



on grasses by the greater proportionate 

 length. 



The structure of the black spores 

 (teleutospores) can be made out with- 

 out difficulty. Some should be found 

 attached at the base. Note the parts 

 and the differences in color in different 

 portions. Make careful drawings to 

 show shape and structure of both kinds 

 of spores. 



Boil a portion of a rust-injured plant 

 in potash solution, pick it to pieces 011 

 a slide under the magnifier or dissect- 

 ing microscope, use a cover-glass and 

 examine the preparation for mycelium, 

 using a high power. 



313. Cultivation on a Host-Plant. 

 If practicable, find some wheat or grass 

 which has remained over winter with 

 the black rust upon it. Tie a bunch 

 of this to a barberry bush while the 

 leaves are young or unexpanded. When 

 the time arrives for the appearance of 

 the cluster-cups, note whether they are any more abundant on this 

 bush than on others. Are you sure that the rust you have is the 

 one to which the barberry cluster-cups belong ? 



FIG. 193. A Group of Spores 

 of Wheat Bust (Puccinia 

 graminis). ( x about 440.) 

 u t 11, uredospores ; t, a teleu- 

 tospore. 



