144 PYRENOMYCETES [CH. 



cells; there is no sign of an antheridium. Nuclear division without wall- 

 formation takes place in the archicarp so that each cell contains two or 

 occasionally three nuclei. At a later stage, after abundant branching, the 

 young perithecium contains a number of binucleate cells; from these the 

 asci arise, the hypha bending over and cutting off a binucleate subterminal 

 cell in the usual way. No fusion but that in the ascus was observed by 

 Moreau. The chief interest of this life history lies in the origin of the bi- 

 nucleate condition, as in some Basidiomycetes, by nuclear division. 



In Melanospora the stroma may be absent, but when present is charac- 

 teristically fleshy; the perithecium neck is elongated; the species occur on 

 the fructifications of the Pyrenomycetes, on those of Pezizaceae and 

 Tuberaceae, on various plant remains and in one or two cases on living 

 plants; thus M. damnosa may be a serious disease on wheat and rye. 



The development oi M. parasitica was studied by Kihlman; this species 

 is a parasite on certain fungi parasitic on insects, including Cordyceps militaris, 

 which is itself a member of the Hypocreaceae. 



The first sign of the development of perithecia is the yellow coloration 

 of the mycelium, which has hitherto been white. 



The archicarp is a stout, twisted, multicellular hypha forming two or 

 more coils and ending in a somewhat pointed cell; its growth is renewed 

 after the development of the sheath has begun and it divides into some 

 fifteen cells; one of these, which may be termed the ascogenous cell, divides 

 in three directions, forming a true tissue from which the asci arise. 



Melanospora Zobelii'^ is parasitic on various fungi and especially on the 

 disc of certain Pezizaceae; Nichols found that the spores germinate to give 

 rise to a mycelium in the cells of which the nuclei are arranged more or less 

 in pairs^. The archicarp is a coiled or curved branch which becomes septate; 

 near it a more slender antheridial hypha may develop, and, in some cases, 

 may fuse with the female organ. 



Vegetative hyphae give rise to a sheath of the usual type with an outer 

 layer, two or three cells thick, of thick-walled, isodiametric cells, and an inner 

 layer of laterally compressed tubular cells; within this is a loose spongy 

 parenchyma of cells rich in contents from which the asci arise. A connection 

 between the archicarp and the asci has not been traced, but it seems probable 

 that the whole central tissue of the perithecium may be derived from the 

 divisions or branches of the archicarp perhaps, as in M. parasitica, by means 

 of an ascogenous cell. 



A further study of the development of the perithecium and especially of 

 the origin of the asci in this genus is much needed. The facts, especially in 

 M . parasitica, suggest that the divisions of the archicarp after the develop- 



' Melanospora Zobelii (Corda) Fuckel = Ceratostoma brevirostre Fuckel. 

 ^ Presumably owing to rapid division ; cf. p. 47, ante. 



