232 ASCOMYCETES. 



but are rarely found in natural conditions ; as yet infection 

 with these has had no result.) 



[Eeniedial treatment must be promptly applied. Trees liable 

 to attack should be frequently examined, so that any young 

 knots may be early removed. If the disease is of long standing, 

 the only remedy left is to remove all knotted branches and 

 burn them immediately.] (Edit.) 



HYSTEEIACEAE. 



The ascocarps of the Hysteriaceae, like those of the Discomy- 

 cetes, are known as apothecia. They are distinguished from 

 those of . the Pyrenomycetes and Perisporiaceae in that 

 the ascocarp, although formed in or under the epidermis of 

 attacked plant-organs, is not a closed structure or flask opening 

 by a pore only ; it is, indeed, at first completely closed, but 

 later it, as well as the epidermis covering it, splits open and 

 freely exposes the whole hymenium. So long as the apothecium 

 is closed, it is iilled with paraphyses, between which the 

 developing asci gradually wedge themselves. The spores 

 are generally thread-like, with a gelatinous membrane. The 

 mycelium lives intercellular, and is often parasitic in living 

 plants. The apothecia, however, only reach maturity on parts 

 which have been killed. In addition to apothecia, little pycnidia 

 (spermogonia) are formed, containing small unicellular conidia. 

 The Hysteriaceae include the Hysterineae, Hypodermieae, Dichae- 

 naceae, and Acrospermaceae. 



HYSTERINEAE. 



Hysterographium. 



Apothecia black, highly vaulted, and dehiscing by a linear 

 fissure. The asci are club-shaped and thick-walled ; they con- 

 tain eight multicellular spores, which are at first transparent, 

 but later dark-coloured. The branched paraphyses of the 

 upper part form a coloured epithecium.^ 



Hysterographium fraxini (Pers.) (Britain). This occurs on 

 various Oleaceae and some other species of woody plants. 



'The exoipulum of De Bary. 



