192 THE ASCOMYCETES 



from which they arise. On rye, they are 1 to 3 cm long; on 

 MoUjiia coenilea, 4 to 6 mm; on Foa pratensis, 6 mm; on Elynms 

 canadensis, the same size as on rye. 



The sclerotia mature at harvest time and normally fall to the 

 ground, where they hibernate. If they are harvested and stored 

 with the threshed grain, they may be returned to the field wdth 

 the seed. Tulasne (1853) found that the minimum dormant 

 period is 3 months. Kirchhoff (1929) reported that after several 

 weeks' exposure to cold, followed by a similar period of higher 

 temperature, germination may ensue. He secured 60 to 80% 

 germination after 4 to 8 weeks' exposure at 15° C. If the period 

 of exposure was short, germination proceeded tardily. If the 

 sclerotia w^ere stored in the cold, at a temperature near freezing, 

 for 2 months, satisfactory germination ensued after 3 to 4 weeks' 

 exposure at the higher temperatures. Burial in moist sand consti- 

 tuted a favorable substratum for germination. 



Zimmerman (1906) noted that sclerotia usually germinate dur- 

 ing May of the year following that in which they were formed. 

 They may remain dormant, however, until the second year and 

 then germinate at the normal season. Germination is first evi- 

 dent as bulges in the sclerotial cortex. These bulges burst through 

 the rind and develop into the clavate stromata, which consist of 

 slender stalks surmounted by spherical heads, 1 to 1.5 mm in 

 diameter. The entire stroma is yellowish white at first but 

 changes to grayish violet. The stromata that arise from a sclero- 

 tium may vary in number from a few to more than a score. At 

 maturity the head of each is covered with wart-like projections 

 that mark the position of the innate, pear-shaped, perithecial 

 locules with orifices at the tip. 



Details of the formation of perithecia were first elucidated by 

 Killian (1919). He described pairs of branches, one an antherid- 

 ium, the other an ascogonium, which formed on the top of pe- 

 culiar voluminous cells and became the primordia of ascogenous 

 hyphae. The antheridia and ascogonia are surrounded by fun- 

 gous parenchyma that fills the locules. Eventually the paren- 

 chyma cells are entirely replaced by asci and paraphyses. Each 

 ascus contains 8 filamentous spores 50 to 75 \i long and 0.6 to 

 0.7 |i in diameter. Numerous paraphyses are interspersed among 

 the asci. 



