28 Notes on Parasitic Ascomycetes. — III. [Sess. 



elliptical, hyaline spores, which become divided into four or 

 more cells at maturity. Another but less common species — 

 D. faginea (Pers.) Fr. — resembles considerably D. quercina in 

 general appearance, but occurs on living bark of beech- 

 branches ; while others are reported to grow on bark of hazel 

 and sallow. 



The last group to be noticed is the Discomycetes, which 

 contain a very large number of species, most of which occur 

 only on dead branches, stems, leaves, or other decaying veget- 

 able matter. Some, however, are true parasites ; while others 

 are mainly saprophytic, but have the reputation of occasion- 

 ally varying their diet by attacking the living tissues of trees 

 or plants. 



In the Discomycetes the asci or spore-bags are not enclosed 

 within perithecia, but are merely embedded in the substance 

 of the ascophore itself, the hymenium or fertile surface of 

 which is fully exposed at maturity. "When an ascus is ripe, 

 it ruptures at the apex, and the spores are thus liberated. In 

 some of the larger species this process of spore-ejection may 

 actually be witnessed when the fungus is placed in bright 

 sunshine. As the asci discharge their contents in rapid suc- 

 cession, the liberated spores are seen to rise into the air in the 

 form of a cloud of minute particles. 



The numerous species of Discomycetes differ widely in size, 

 shape, and other external characteristics ; but in the great 

 majority the spore - bearing surface (otherwise known as 

 the " hymenium ") is expanded in the form of a cup or disc. 

 Another type, however, is afforded by the Phacidiacese, in 

 which the hymenium is at first covered by the upper surface 

 of the ascophore, but is finally exposed by the splitting of the 

 covering, which is usually effected in a radiate manner. Of 

 this type several illustrative examples may be referred to. 

 One of the most interesting is Keithia tctraspora (Phil. & 

 Keith) Sacc, discovered many years ago in the north-east of 

 Scotland by the late Rev. James Keith, LL.D., Forres. It 

 occurs on brownish-yellow spots on the upper surface of green 

 leaves of Juniper. As each specimen becomes mature, the 

 surface of the spot splits irregularly into three or four laciniae 

 or teeth, and discloses a hymenium which is black at the 

 surface but brownish-yellow within. At this stage it is said 



