276 GENERAL BOTANY 



The black-rust spores, called teliospores or teleutospores, are 

 formed in the same sori and from the same mycelium as the 

 red rust, but are produced later in the season than the latter. 

 The black-rust spores are two-celled, thick-walled wintering 

 spores (Z>) which live through the winter on the straw or stubble 

 and germinate the next spring after their production. Their 

 germination (JS) results in small spores, usually called sporidia 

 (s), which are blown to the young leaves of the barberry and 

 start a mycelium for the production of a fresh crop of aecidium 

 cups and spores on the barberry leaves. 



This completes the remarkable cycle of these peculiar plants, 

 which have become so highly adapted in their spore forms to 

 the seasonal life of the organism. This seasonal life, as the 

 above account indicates, comprises two distinct feeding mycelial 

 plants, which grow on two different species of flowering plants. 

 Four kinds of spores are also produced, which serve for dissemi- 

 nating the plants in spring and summer and for wintering. 



Other forms of rusts occur on various cereal grains and on 

 the grasses, to which the cereals are closely related. Not all of 

 these rusts, however, have so complicated a life history as that 

 of Puecinia graminis, although most of them have at least two 

 forms of spores and many species avail themselves of two hosts 

 in the production of these spores. The rusts are among the 

 most destructive of the fungi and cause the loss of many 

 millions of dollars each year by the damage to cereals of 

 various kinds. 



SMUTS 



The most familiar smut is that of Indian corn ( Ustilago zeae) 

 (Fig. 154), which causes the distortion of the kernels of corn on 

 the cob and produces the large black masses of smut spores seen 

 in fields of corn in the autumn. If the smutted ears of corn are 

 examined early in the season, it will be found that the fungus 

 gradually replaces the kernels as it absorbs the food stored in 

 them. Later the infected kernels grow to many times the size 

 of the original kernels and produce great masses of spores in 

 cavities which resemble somewhat those already described in 



