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.