GARPOPHTTA. 173 



um). In many species the round of life is like 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. 



A teleutospore is here regarded as one or more spores contained in 

 a thin-walled and tightly fitting spore-sac. It is therefore to be com- 

 pared with the spore sacs of the previous orders (Figs. 88, 89, 92), and 

 its simplicity is to be regarded as due to the excessive parasitism of the 

 rusts. The Black-rust stage is thus a degraded spore-fruit, in which 

 the spore-sacs are not compacted into a well-defined fruit-like body. 



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

 berry, 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. 



(J) 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. 94, A and I.) 



ic) 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 liltle stalks. (Compare with Fig. 94, 

 //, 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 sections of the leaf also (Fig. 94, III). 



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

 of rotting straw. Look for germinating teleutospores and sporids 

 (Fig. 95, 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. Their cluster-cups 

 occur on apple-leaves. 



358. The Smuts (Order TTstilaginecB). The plants which 

 compose this order are all parasites living in the tissues of 

 flowering plants. Like the Rusts, they send their parasitic 

 threads through the tissues of their hosts, and afterwards 



