EU-MYCETES.- (&) BASIDIOMYCETES 443 



colour of rust of iron. They are found in sueh quantity as to attraet 

 public attention, and this has provided tlie name. 



The most familiar example, as it is also economically the most 

 important, is the Rust of Wheat, Puccinia graminis. In June and 

 July the green leaves of the Wheat are often seen to lose their colour 

 (^^"'g- 375)- Yellow patches appear between the veins, and run 

 together into Imcs that follow the softer mesophyll. The epidermis 

 bursts, and innumerable orange spores are set free, which are easily 

 carried as dust by the wind. These are the Uredo- or Summev-spores 

 of the Rust. A part of a field thus diseased is a centre of infection, 

 and the fungus may often be seen to spread from it down the prevailing 



Fig. 376. 



Part of shoot of Barberry with leaves attacked by Accidhtm Berhcridis, which fonus 



yellow cushions on the leaf-blades and stalks. (After Marshall Ward.) 



wind. This production of spores, which represents so much material 

 robbed from the developing crop, may continue till autumn ; but 

 gradually the patches of disease change in colour to a dark purple- 

 brown. This is due to the formation in them of a new kind of spore, 

 the Winter- or Teleuto-spore, which is firmly attached to the straw, 

 and dies down with it, or is removed with the crop. These spores 

 retain their vitality till the next spring, when they germinate 



(Fig. 375). 



The result of their germination has been shown experimentally 

 to be the infection of the leaves of the Barberry plant, and the pro- 

 duction of a second stage, which appears as red or yellow blotches, 

 thicker than the healthy parts of the leaves that bear them : small 

 dark spots open on the upper surface [spermogonia), and numerous 

 widely gaping cups (aecidia) are clustered together on the lower 



