As is clear from the above, nearly all the lichens are produced by the association of an ascomycetous fungus with algae.
The so-called Gasterolichens, Trichocoma and Emeri- cella, have been shown to be merely ascomycetous fungi.
A widespread disease known as pocket-plums or bladderplums is due to an ascomycetous fungus, Exoascus pruni, the mycelium of which lives parasitically in the tissues of the host plant, passes into the ovary of the flower and causes the characteristic malformation of the fruit which becomes a deformed, sometimes curved or flattened, wrinkled dry structure, with a hollow occupying the place of the stone; the bladder plums are yellow at first, subsequently dingy red.
