PLAXTS WHICH CAl'SE BBC AT 



•iU.'l 



a mycelium which spreads rapidly through the Iiaf aud 

 finally forms spores known as cluster-cup spr)rH> (or 

 secidiospores). These spores, as their name 

 implies, are arranged in clusters in cup- 

 like cavities of the leaf (Fig. 228), which 

 are produced by their growth. On exam- 

 ining thin sections of the leaf carefully, we 

 see that the cluster- cup spores are in long 

 chains borne on short stalks (Fig. 229). 

 On the upper surface of the leaf occur 

 smaller cavities filled with smaller slender 

 spore-bearing stalks; their function is not 

 understood. We see, then, that the Black 

 Stem Rust of the Wheat occurs in three 

 difiierent forms, at different times of the 

 year — the uredospores in the summer, the 

 teleutospores in the autumn, and the clus- 

 ter-cup spores on Barberry in spring. Formerly, when 



it was not known that 

 these were all forms of 

 the same fungus, they 

 were described as sepa- 

 rate genera. The discov- 

 ery that the Barberry had 

 something to do with the 

 Rust on Wheat was first 



Autiimn spores 

 ot the Black 

 Stem Rust of 

 Wheat pofiuc- 

 Liigcoindia(c). 



22«. Section of Barberry leaf, showing the Uiaile by praCtical fami- 

 eluster-cup stage of Black Stem Rust of 

 Wheat. 



ers, who observed that 



