282 



GENERAL MORPHOLOGY OF PLANTS 



448. The red rust of wheat (uredo stage). The aecidio- 

 spores from the cluster cup on the barberry are carried by the wind 



Fig. 249. 



Section through leaf of barberry at point affected with the cluster-cup stage of the wheat 

 rust; spermogonia above, aecidia below. (After Marshall-Ward.) 



to the wheat (also to the other cereals and some grasses). Here 

 they germinate and the mycelium enters at a stomate and pro- 

 duces the intercellular mycelium. At certain points under the 



Fig. 250. 



Fertilization and development of aecidiospores in a rust, Phragmidium violaceum. ep, 

 epidermis of host. st, sterile cells at ends of a-cidial thread, fc, fertile cells. A, part of 

 aecidial stroma, showing two binucleate, fertile cells. B, showing nucleus of sperm cell at base 

 of fertile cell passing into the fertile cell at the side. C, similar stage. D-G, different stages 

 in formation of aecidiospores. H, mature aecidiospore. (After Blackman.) 



epidermis of the leaf, or stem, a group of short spore-bearing 

 hyphae are formed, each of which bears a broadly elliptical spore 

 with minute warts on the wall, and with a yellowish oil in the proto- 

 plasm. These spores are the uredos ports. The pustule formed 



i 



