THE FUNGI WHICH CAUSE PLANT DISEASE 213 



60-70 II. long. Conidia (=Sphacelia segetum) produced on the 

 grain before the sclerotium is formed, conidiophores short, cylin- 

 dric, arranged in a compact palisade, bearing small, oval, hyaline, 

 1-celled conidia. Hosts, rye, wheat, oats and numerous other 

 grasses. 



Infection of the ovary at blooming time is followed by complete 

 possession and consumption of the ovarial tissue by the myceUum, 

 and by considerable development of stroma beyond the ovary. 

 On the external much-folded part of this stroma, particularly at 

 its distal end, are borne layers of conidiophores and numerous 

 conidia and a sweet fluid is exuded. The conidia, carried by in- 

 sects, spread summer infection. Later the stroma, losing a large 

 . part of the distal region, rounds off to a definite sclerotium, smooth, 

 firm, blue to black in color, and several times larger than the 

 normal grain of the host plant. 



After a period of rest, usually lasting till the following season, 

 the sclerotium gives rise to several stalked, capitate, perithecial 

 stromata. The perithecia are arranged around peripherally, the 

 ostioles protruding and giving the head a rough appearance. The 

 sclerotium constitutes the ergot of pharmacy and contains a 

 powerful alkaloid capable of causing animal disease if eaten. 



This species appears to be differentiated into a number of 

 biologic races. ^^* 



C. microcephala (Wal.) Tul. infects niunerous grasses both in 

 Europe and America, being especially destructive to blue grass. 



Two species C. paspall S. & H. and C. rolfsii S. & H. have been 

 reported on Paspalum.^** 



Ustilaginoidea Brefeld (p. 199)i" 



Sclerotium formed in the grain of the host, resembling super- 

 ficially a smut sorus, in the center composed of closely interwoven 

 hyphffi, externally the hyphse are parallel, radiating towards the 

 periphery and bearing echinulate, globose, greenish conidia; stroma 

 with a long sterile stem and a fertile head; perithecia immersed 

 in the stroma as in Claviceps; asci and spores also as in Claviceps. 



Two species are known, one on Setaria which produces an 

 ascigerous stage, the other on rice, the ascigerous stage of which 



