THE WHEAT RUST 



69 



99. Other Rusts of Cereal Grains. — As a group, the rusts have 

 been remarkably successful in adapting themselves to a parasitic life 

 — parti}', no doubt, because of 

 the number and varietv of 

 spores that they oroduce. So 

 successful have ttiey been that 

 most of the species of seed- 

 bearing plants are attacked 

 each by one or more species of 

 rust. Some rusts seem to have 

 become so specialized as to be 

 able to live upon only one or a 

 very few hosts; in other in- 

 stances, a single rust may 

 attack a considerable number 

 of hosts.' Besides the common 

 wheat rust which has been 

 described in this chapter and 

 which is called Puccinia grami- 

 nis, there are at least two 

 other rusts that infect the 

 wheat. All the other cereal 

 grains, too, are attacked by 

 rusts, some of which cause large 

 losses. The known grain rusts, 

 in addition to Puccinia grami- 

 nis are : the crown rust, one 

 of whose races or varieties 

 causes a serious disease of oats ; 



the yellow rust, races of which attack wheat, barley, and rT.-e ; the brown 

 rust of r\-e ; the brown rust of wheat ; the dwarf rust of barlev ; and 



1 A word of caution should accompany this statement. In some cases the rusts 

 appearing upon two or more hosts seem to be exactly aUke, but the spores produced 

 by the rust upon one host will not iniect the other host, and rice versa. Thus, there 

 are rusts on rye, oats, barley, and several common grasses which appear to be the 

 same as that upon the wheat and which are railed by the same name (Puccinia 

 graminis). But the summer spores of the wheat rust will not infect the oat at all, 

 or only with great difficulty, and in the same way summer spores from Puccinia 

 graminis on oats will not infect the wheat, although both the rust on wheat and 

 that on oats pass their spring stage upon the barbem-. These facts have given 

 rise to the notion of specialized races of parasitic fungi. Two such races may seem 

 to have exactly the same structure, but they differ in that they have adapted them- 

 selves in some way to life upon different hosts. 



Fig. 30. — .\ branch of the red cedar 

 bearing two "cedar apples" — sweUings 

 caused by the presence of a rust — in 

 the winter condition. After Jones and 

 Bartholomew. 



