SEXUALITY OF SMUTS 



303 



occurs in U. zeae on corn. (3) Infection through stigmas, in 

 which the smut spores lodge on the stigmas, penetrate them, and 

 remain within the ovary as a dormant mycehum. When such 

 infected seed germinate, infection becomes systemic and sporula- 

 tion again occurs when the 

 host flowers. Infection of this 

 kind is exhibited by U. tritici, 

 the cause of loose smut of 

 wheat, and by U. niida, caus- 

 ing naked smut of barley. 

 (4) Infection through tiller 

 shoots, such as may occur in 

 Urocystis occulta, causing hid- 

 den smut of rye. 



Sexuality of smuts. Among 

 those who have studied the 

 sexuality of smuts are Harper 

 (1898), Lutman (1910), Ra- 

 witscher (1912, 1922), Kniep 

 (1919), Bauch (1925), Stak- 

 man and Christiansen (1927), 

 Rodenheiser (1929), Hanna 

 (1929), Sleumer (1931), and 

 Holton (1932). In regard to 

 the fusion of a pair of nuclei 

 in the maturing chlamydospore 

 all are in accord, but in the 

 manner in which the binu- 

 cleate condition arises there 

 appears to be considerable di- 



FiG. 117. Tilletia tritici. A. Germi- 

 nation of chlamydospore, produc- 

 tion of primary filamentous spo- 

 ridia from which secondary sporidia 

 arise. B. Fusion of primary spo- 

 ridia with hvphal formation. C. Por- 

 tion of branched hypha bearing sec- 

 ondary sporidia. 



versity among various species. 



The observations of Harper (1898) on Ustilago scabiosae show 

 that on germination the diploid nucleus migrates into the pro- 

 mycelium at a time when it has attained approximately one-third 

 of its final length. Bv the time that the promycelium is fully 

 grown, the diploid nucleus has divided meiotically, and 4 haploid 

 nuclei have formed. Septations then appear, resulting in 4 uni- 

 nucleate cells that give rise to lateral buds, the sporidia. Each 

 bud is uninucleate, and each promycelial cell may produce simi- 

 lar sporidia indefinitely. Moreover each sporidium may sprout 



