Bodies closely resembling the perithecia of Sphaeriaceous Fungi have often been observed on impressions of Palaeozoic plants, and may probably belong to the group indicated.
This form of fruit is succeeded by others which have received different names, and lastly by the mature Nectria which forms minute red flask-shaped perithecia on parts of the rotted potatoes that have dried up. The intermediate forms are known as Monosporium, Fusarium and Cephalosporium.
In other cases (Hypomyces, Nectria) the perithecia arise on an already mature stroma, while yet more numerous examples can be given (Poronia, Hypoxylon, Claviceps, &c.) where the perithecia originate below the surface of a stroma formed long before.
The simpler forms bear the perithecia directly on the mycelium, but the more highly developed forms often bear them on a special mycelial development - the stroma, which is often of large size and special shape and colour, and of dense consistence.
The cytological details of development of the perithecia are not well known; most of them appear to develop their ascogenous hyphae in an apogamous way without any connexion with an ascogonium.