GENERAL MORPHOLOGY OF PLANTS 



Fig. 259. 

 Barberry leaf with two 



diseased spots, 

 size. 



Natural 



462. The cluster-cup stage on the 

 barberry. The diseased spots on the leaves 

 of the barberry are yellowish and round. 

 Upon the under side of the leaf there can 

 be seen minute cup-shaped structures 

 (aecidia) distributed over the spots. These 

 are better seen with the aid of a pocket lens. 

 In figures 262, 263, a section of the barberry 

 leaf through one of these spots shows its re- 

 lation to the 

 host and the 

 mycelium be- 

 tween the cells. 

 The cup is 

 formed of a 

 bundle of stout 

 hyphae with 

 stout short 

 cells growing 

 out from this 

 mycelium and 

 The hyphae of the 



Figs. 259-261. Cluster-cup stage of wheat rust. 



Fig. 260. Fig. 261. 



t Single spot, show- Two cluster 



ing cluster cups cups more en- 

 enlarged, larged, showing 

 split margin. 



bursting through the epidermis of the leaf. 



outer layer are sterile, and 



remain united laterally to 



form the wall of the cup, 



which is first closed over 



the top but later opens 



out. The cells of the 



central bundle of hyphae, 



in chains, separate at 



maturity and form the 



cluster-cup spores (aecidio- 



spores). 



Fig. 262. 



Section of an aecidium (cluster cup) from barberry 

 leaf. (After Marshall-Ward.) 



Fertilization takes place by the fusion of two cells in adjacent rows at the 

 bottom of the young cluster cup in some cases, and by the migration of a 



