Parasitic Fungi of Illinois. 389 



these swells to two or three times the diameter of the thread, 

 and is separated from it by a transverse partition. It now con- 

 stitutes the carpogonium, homologous with the pistil of the 

 flowering plants. The other branch, the antheridium, remains 

 cylindrical, and is closely applied to the carpogonium, bending 

 over its summit. A septum is formed near the tip, dividing off 

 a small cell, whose contents, passing into the carpogonium, 

 effect its fertilization. Slender branches now arise on all 

 sides from near the base of the carpogonium. They become 

 branched and septate, and soon join together, forming a mem- 

 branous, cellular, enveloping wall. An inner membrane or 

 coating is developed by short projections branching from the 

 inner wall. The carpogonium is divided by a cross parti- 

 tion, and the upper portion develops into the suborbicular 

 ascus containing the spores, which with its enveloping mem- 

 branes constitutes the sporocarp, or true fruit of the fungus. 

 In the genera having several asci the carpogonium is more 

 elongated, and is bent around the antheridium. After fer- 

 tilization, the enveloping wall develops as above. The car- 

 pogonium becomes divided by cross partitions into a number of 

 cells, each of which either develops directly into an ascus, or 

 sends up an ascus-bearing branch. In all cases the spores de- 

 velop within the asci by free cell-formation. 



Figure 1. SjjJw rotlieca Castagnei, L£v. 

 I., Process of fertilization : a, a thread of 

 the mycelium bearing the oogonium c; b, b, 

 another filament of the mycelium bearing 

 the antheridium d. II., same as I., at a later 

 stage of growth, the oogonium c and anthe- 

 ridium d still seen, the former becoming in- 

 closed by the mycelial branches e. III., a 

 still later stage of same, the oogonium c being now completely inclosed 

 within the tissue forming the mycelial branches, the wall of the young 

 carpogonium. Magnified 300 times. (After De Bary.) 



This act of fertilization does not usually take place till late 

 in the summer. The sporocarp resulting from it is called in 

 this group, the perithecium. When quite young it is colorless, 

 but it soon becomes yellowish, and when mature is a dark brown 

 or black, usually globular, body, visible to the naked eye. Its 

 wall consists of a rather tough membrane, whose cellular struc- 



