Order 4. Acrospermaceæ.
Family 5. Discomycetes.
The ascocarps (apothecia) are at first closed, and only open at the time of their ripening, not valvularly, but more or less like a saucer or cup, so that the hymenium lies exposed on their upper surface. In the first three sub-families, and generally also in the fourth, the apothecia are formed inside the substratum. The apothecia are, in contrast to the Pyrenomycetes, light and brightly coloured, and their size varies very much, and may be several centimetres in diameter. Paraphyses are often present between the asci; they often contain colouring matter, and give to the disc its characteristic colour. The tissue on which the asci are borne is known as the hypothecium. The shape and colour of the spores is not so varied as in the Pyrenomycetes. The accessory forms of reproduction are conidia (sometimes of two forms), chlamydospores, and oidia. The family is divided into 5 sub-families.
Sub-Family 1. Phacidiales.
The apothecia are developed in the interior of the substratum, which they break through, and in general dehisce apically. The envelope is tough and black. Hypothecium inconspicuous; hymenium flat.
Order 1. Euphacidiaceæ. Phacidium abietinum, on the leaves of Abies alba.—Rhytisma; the pycnidia are found in the summer on the green leaves, while the apothecia are developed on the fallen leaves and dehisce in the following spring. R. acerinum causes black spots on the leaves of the Sycamore, and R. salicinum on Willows.
Order 2. Pseudophacidiaceæ.
Sub-Family 2. Stictidales.
The apothecia when ripe break through the substratum which forms a border round them. Hymenium generally saucer-shaped.
Order 1. Stictidaceæ. Stictis.