FUNGI, THE RUST FUNGI 315 



divides quite regularly by three cross walls into four cells, each 

 of which forms a small pointed process.* Through this process 

 the protoplasm in the cell moves out and forms a small spore. f 

 This small spore is carried by the wind to the barberry, where 

 it germinates, the tube enters through the epidermis (fig. 276) 

 into the barberry leaf, and starts the cluster-cup stage again, thus 

 completing the life cycle. 



466. Races of the wheat rust* There are some peculiarities in the life 

 of the wheat rust, which as stated above occurs on oats, barley, rye, and many 

 grasses. For example, the uredospores formed on the oats can infect oats 

 but cannot infect wheat, rye, barley, and some grasses; and the same is true 

 with the uredospores from the barley, rye, and some of the grasses they can- 

 not infect the oats and members of the other groups. The uredo- and teleuto- 

 spores on these different plants cannot be distinguished as to form, size, etc. 

 They constitute physiological races which have become confined to certain 

 groups of hosts. In the case of all of these races, however, the sporidia from 

 the teleutospores can produce the cluster cups on the barberry. But cluster 

 cups originating from oat teleutospores cannot infect wheat, barley, rye, etc., 

 but only oats and the members of the oat group. 



467. How the wheat rust passes the winter in regions 

 where the barberry is absent. It has long been known that the 

 wheat rust can live through the winter in the teleutospore stage. 

 Since the sporidia from the teleutospores cannot infect the cereals 

 or grasses buf only the barberry, the appearance of the wheat 

 rust in early spring, in regions where the barberry does not exist, 

 has long been a mystery. It is well known that in southern lat- 

 itudes, as in the Gulf States in America, and along the Mediter- 

 ranean coast in Europe, the wheat rust can live through the win- 

 ter in grains and grasses in the uredo stage, since the climate is 

 so mild. This led to the belief that southern winds in the spring 

 bore the uredospores northward and thus produced sudden and 

 widespread infection in northern latitudes. This probably does 



* Sterigma. 

 J" Sporidium. 



