DISCOMYCETES. 133 



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 kypotliecium . The shape and colour of 

 the spores is not so varied as in the Pyrenomycetes. The acces- 

 sory 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. Euphacidiaceae. Phacidnim abietinum, on the leaves of Abies 

 alba. Rhytisma; the pycnidia are found in the summer on the green leaves, 

 while the apothecia are developed oil the fallen leaves and dehisce in the 

 following spring. R. acerinum causes black spots on the leaves of the Syca- 

 more, and R. salicinuin on Willows. 



Order .2. Pseudophacidiaceae. 



Sub-Family 2. Stictidales. 



The apothecia when ripe break through the substratum which 

 forms a border round them. Hymenium generally saucer-shaped. 



Order 1. Stictidaceae. Stictis. 

 Order 2. Ostropaceae. Ostropa. 



Sub-Family 3. Tryblidiales. 



The apothecia are embedded in the substratum in the early 

 stages, and then are raised high above it. Hypothecium thick. 

 Hymenium cup-shaped. 



Order 1. Tryblidiaceae. Tryblidium. 



Order 2. Heterosphaeriaceae. Heterospluzria patella on the dead stalks 

 of Umbellifers. 



