ASCOMYCETES 245 



The fungus. The fungus shows an interesting polymorphism, 

 first producing a conidial stage upon the ovule sac, later the 

 sclerotial or true ergot stage in place of the grain, and finally 

 completing its life cycle by developing special sporophores from 

 this sclerotium after a long period of rest has .been undergone. 

 The fungus is supposed to gain entrance to the host at the base 

 of the ovule sac or carpel, penetrating the latter and developing 

 through it or over it as a hyphal weft, or primary mycelium, the 

 whole structure maintaining the general shape of the ovule sac, 

 which is gradually replaced by the fungous body. The surface 

 mycelial areas are thrown into folds and numerous short conidio- 

 phores arise, bearing small ovate conidia. This is known as the 

 sphacelial stage. Insects are attracted to it by a secretion, and 

 the spores are by this means 

 and by the wind effectively 

 disseminated. Meanwhile, a 

 dense growth of the fungus 

 makes its appearance at the 

 base of the affected part and 

 gradually enlarges as a firm, 

 compact body, or sclerotium. 



It gradually replaces the area FlG " I0 5- CLAVICRPS PUHPURBA: SCLERO- 



. * TIUM WITH STROMATA 



occupied by the sphacelial 



stage, becomes purplish in color, and in time projects beyond the 

 usual dimensions of the normal ovule sac, pushing forward upon 

 its tip the remnant of the sphacelial stage and any portions of style 

 and stigma which may remain. The sphacelial stage and the rem- 

 nants of the ovule sac are finally brushed away or fall off and the 

 mature sclerotium is in the form of a very hard, purplish or brown, 

 slightly curved or horn-shaped body, which may attain a length of 

 from one half to one and one-half inches (Fig. 105). The develop- 

 ment of this sclerotial stage requires about the same length of time 

 as is needed for the development of the grain in the normal ovule 

 sacs. It is therefore mature at the time that the grain is mature. 



The sclerotium readily falls from its place of production and 

 must then undergo a long period of ivst bi-foiv it is in condi- 

 tion to be brought to germination. In this particular speck's ger- 

 mination in nature apparently results early the following spring. 



