THE FUNGI 399 
basidiospores arise. (Fig. 296.) The basidiospore, upon coming 
in contact with young growing tissue or a wound upon the host 
plant, starts a new infection and develops a mycelium which 
penetrates the infected organ. 
ORDER 2.—UREDINALES, the rusts. Obligate parasites 
possessing a septated, branched mycelium which ramifies 
a 
Ai 4 
N a 
Fic. 296.—Germination of the chlamydospores of corn smut (Ustilago zee); 1, 
Various stages in germination from corn 3 days after being placed in water; 2, 
spores germinated in contact with air; 3, several days after spores were placed in 
140 per cent. acetic acid, formation of infection threads. a, Spores; 6, promycelia; 
c, basidiospores; d, infection threads; e, detached pieces of mycelia. (After Bull. 
57, Univ. Ill. Agric. Exper. Stat., March, 1900.) 
through the intercellular-air-spaces of the host and _ sends 
haustoria into the cell cavities. The different stages of their 
life cycle are either restricted to one host or distributed between 
two or more hosts. An outline of the life history of the wheat 
rust will give an idea of the peculiarities of the group. 
Tue Wueat Rust (PucctntA GRAMINIs).—If we examine the 
wheat plant just before harvest we will find on the stems and 
