CHAPTER XXII. 



FUNGI (CONTINUED) : WHEAT RUST. 

 (Puccinia graminis.) 



215. Importance of the rusts. The fungi known as " rusts " 

 are very important ones to study, since all the species are para- 

 sitic, and many produce serious injuries to crops. 



Exercise 45. 



216. Black rust of wheat. Dried stalks of wheat or oats with the black 

 spots of this stage of the rust are excellent for the study. Sketch a portion of 

 an affected stalk, showing the spots in natural size and form. With a hand 

 lens examine the spots more carefully. Observe that the black mass of color 

 has burst through the epidermis of the wheat. Describe the" appearance. 



217. Red rust of wheat. This stage is found abundantly on the leaves of 

 the wheat and oats, etc. Dried leaves which have been pressed are good 

 for the study. Observe the color of the spots, and compare with that of the 

 black-rust spots. Compare the size also. Examine with a hand lens, and 

 determine whether the mass of spores making up the rust color, break through 

 the epidermis. Sketch a portion of the leaf showing the characters observed. 



218 . Cluster-cup stage on the barberry. Leaves of the barberry maybe 

 pressed dry and preserved for study. Sketch a leaf showing the location and 

 character of the spots. Describe the form and character of the spots. Ex- 

 amine the spots on both sides of the leaves with a hand lens. Describe what 

 you see. If leaves of the barberry with the cluster cups cannot be obtained 

 some other cluster-cup fungus may be used, but it should be understood that 

 the others are not connected with the wheat rust (except some growing on 

 shrubs closely related to the barberry). 



Demonstration 33. 



219. To demonstrate the different stages of the wheat rust under the micro- 

 scope. Black rust: with a knife scrape out the material from a few black 

 spots, tease out in water on a glass slip, and mount as usual. Red rust : pre- 

 129 



