Examine prepared slides of Cryphonectria parasitica showing sections through a stroma and note the arrangement of perithecia. This species is the causal organism of the disease known as chestnut blight, and was formerly placed in the genus Endothia . These are perithecial fungi with lateral paraphyses and unitunicate asci. The asci are long and cylindrical, with a thickened apex, and they contain eight ascospores. The ascospores are filiform, hyaline, and septate.
Most species are parasitic on grasses, insects, or other fungi.
Claviceps - In this genus, the perithecial stroma develops as a head on an erect stalk and arises from a dark sclerotium. Examine preserved material of Claviceps purpurea , the cause of ergot disease of cereals. Look at prepared slides showing sections through young sclerotia bearing the conidial state, Sphacelia segetum . Also examine prepared slides showing sections through sclerotia bearing perithecial stromata. Note the perithecia, asci and ascospores.