FUNGI: RUSrS. 



131 



courses between the cells, just as is found in the case of the 

 carnation rust, which belongs to the same family (see Part III). 

 291. TJredospores of the red-rust form. — If we make a simi- 

 lar preparation from the pustules of the red-rust form we see 

 that instead of two-celled gonidia they are one-celled. The 

 walls are thinner and not so dark in color, and they are covered 

 with minute spines. They have also short stalks, but these fall 

 away very easily. These one-celled gonidia of the red-rust form 

 are called " uredospores. " The uredospores and teleutospores 

 are sometimes found in the same pustule. 



It was once supposed that these two kinds of gonidia belonged 

 to different plants, but now it is known that the one-celled 

 form, the uredospores, is a form developed 

 earlier in the season than the teleutospores. 

 292. Cluster-cup form on the barberry. 

 — On the barberry is found still another 

 form of the wheat rust, the ''cluster cup" 

 stage. The pustules on the under side of 

 the barberry leaf are cup-shaped, the cups 

 being partly sunk in the tissue of the leaf, 

 while the rim is more or less curved back- 

 ward against 

 the leaf, and 

 split at several 

 places. TJiese 

 cups occur in 

 clusters on the 

 affected spots 

 of the barberry 

 c-:„ ,„ leaf as shown 



Two cluster jn fig. 154- 

 cups more en- 

 larged, showing Within the 

 split margin. 



Figs. 153-155.— Cluster-cup stage of wheat rust. CUpS numbers 



of one-celled gonidia (orange in color, called aecidiospores) are 

 borne in chains from short branches of the mycelium, which 

 fill the base of the cup. In fact the wall of the cup (peridium) 



Fig- 153- 

 Barberry leaf with two 

 diseased spots, natural 

 size. 



Fig. 154- 

 Single spot 

 showing cluster 

 cups enlarged. 



