OARPOPHTTA. 195 



sissippi Valley and on the Great Plains are propagated in this way. 

 It has been shown also that on the Great Plains the red rust is per- 

 ennial, blowing to the north in the spring from field to field, and 

 blowing back to the south in the autumn. Probably this is the more 

 common mode of propagation upon the plains. 



There are many kinds of rusts, distinguished mainly by their te- 

 leutospores, which are single (Uromyces and Melampsora), in twos 

 (Puccinia and Gymnosporangium), or several (Phragmidium). In 

 many species the round of life is similar to that in Wheat-rust, but 

 in others there appears to be a constant omission of certain stages. 

 Moreover, in many species all the stages develop upon the same host- 

 plant. 



Practical Studies. — (a) Collect specimens of cluster-cups (from 

 barberry, buttercups, or evening primrose, etc.) ; examine first under 

 a low power without making sections. Note the cups filled with yel- 

 lowish or orange conidia, (secidiospores). Note spermogones (minute 

 dark spots) generally on the opposite side of the leaf. 



(6) Make very thin cross-sections through a mass of cups so as to 

 obtain vertical sections of the cups and the spermogones. (Compare 

 with Fig. 113, A and I.) 



(c) In June and July collect leaves of wheat, oats, or barley, bear- 

 ing lines or spots of Red Rust. First examine a few of the spores 

 mounted in alcohol, with the subsequent addition of a little potassic 

 hydrate. Then make very thin cross-sections through a rust-spot, 

 and mount as before, so as to see parasitic filaments in the leaf, bear- 

 ing the Red-rust spores upon little stalks. (Compare with Fig. 113, 

 n, ur.) 



(d) In July, August, or September collect stems of wheat, oats, or 

 barley bearing lines or spots of Black Rust, Study the spores as 

 above, and afterwards make cross -sections also (Fig. 113, ///). 



(e) In early spring collect and examine the Black Rust on wet stems 

 of rotting straw. Look for germinating teleutospores and sporids 

 (Fig. 114, A and B). 



(/) Examine microscopically the gelatinous prolongations on "ce- 

 dar-apples," and observe the teleutospores, which resemble those of 

 Wheat-rust. "Cedar-apples," which are common in the spring on 

 Red-cedar twigs, are in reality species of rust of the genus Gymno- 

 sporangium. Their cluster-cups occur on apple-leaves. 



Systematic Literature. — Burrill, Parasitic Fungi of Illinois : Ure- 

 dinese. Saccardo, Sylloge Fungorum, 7'' : 528-882. 



356. The Smuts (Order 17, UsTiLAGiNBiB).^ — The plants 

 which compose this order are all parasites living in the tis- 



