v] HYPOCREALES 145 



ment of the sheath has begun, may correspond to the septation of the 

 fertilized oogonium in other forms. Further, the origin of the asci from a 

 single cell points to the Erysiphales and Laboulbeniales, and in view of the 

 longitudinal divisions, perhaps especially to the latter. 



In Nectria the usually red or yellow perithecia are produced in groups on 

 stromata of the same colour; the asci contain eight ascospores which are two- 

 celled, and often produce conidia by budding while still in the ascus. The 

 genus is large, including some 250 species among which N. cinnabarina, the 

 commonest in this country, is of very frequent occurrence on the living and 

 dead branches of deciduous trees. The mycelium from the germinating 

 spores is unable to penetrate the bark of the host, and infection takes place 

 only through open wounds. Once established, however, the mycelium spreads 

 rapidly especially in the xylem. The cambium and other tissues are not 

 attacked but die as a result of the destruction of the wood, so that as develop- 

 ment proceeds branch after branch is killed. Meanwhile the stromata appear 

 (fig. 105); in the conidial stage they are bright pink and occur at all seasons 



Fie 10 =,. Nectria cinnabarina (Tde.) Fr. on a fallen twig; a. conidial stroma; b. young 

 perithecia; x6; E. J. Welsford del. 



on the dead and living branches; perithecia are produced only in the autumn 

 and winter and only after the tissues have been killed ; they are deep red 

 in colour and are partly immersed in the deep red stromata. When a peri- 

 thecium is about to be formed a coil of hyphae larger than the ordinary 

 filaments of the stroma appears a little below the surface, and probably 

 represents the remains of whatever sexual apparatus originally gave rise to 

 the ascogenous hyphae. 



Nectria cinnabarina is thus one of the rather numerous fungi which pro- 

 duce conidia during their parasitic phase, and ascospores only when the 

 death of the host has rendered them saprophytic. In view of the life-history 

 of this species it is obvious that there are two methods of checking the damage 

 which it does; the burning of infected branches on which the development 

 of the spores takes place, and the painting over of open wounds through 

 which alone the entrance of the mycelium is effected. 



