'3° 



BOTANY. 



pare in the same way from the yellow spots. To demonstrate the cluster cups, 

 good cross-sections of the leaf through a spot should be made, or prepared 

 slides should be obtained. Let the pupils sketch the form of the different 

 spores, and other characters, and make notes of the observations. 



To demonstrate mycelium in the tissues, use the carnation rust which can 

 be obtained in winter in greenhouses where the carnations are grown (see 

 Chapter XV, paragraph 159), or fresh wheat leaves may be preserved in 

 alcohol for making sections. 



220. Wheat rust (Puccinia graminis). — The wheat rust is 

 one of the best known of these fungi, since a great deal of study 

 has been given to it. One form of the plant occurs in long 



\ 



Fig. 102. 

 "Wheat leaf with red 

 rust, natural size. 



Mg. 106 

 Single 



sorus. 



Fig. 103. Fig. 104. Fig. 105. 



Portion of leaf Black rust. Enlarged, 



enlarged to show Natural size, 



sori. 



Figures 102, 103. — Puccinia graminis, red rust stage (uredo stage). 

 Figures 104-106. — Black rust of wheat, showing son of teleutospores. 



reddish-brown or reddish pustules, and is known as the " red 

 rust" (figs. 102, 103). Another form occurs in elongated 

 black pustules, and this form is the one known as the " black 

 rust" (figs. 104-107). These two forms occur on the stems, 

 blades, etc., of the wheat, also on oats, rye, and some of the 

 grasses. 



221. Teleutospores of the black-rust form. — Scrape off some 

 portion of one of the black pustules (sori), tease it out in 

 water on a slide, and examine with a microscope, to see numer- 



