GROUP I. THALLOPHTTA : FUNGI : ASCOMYCETES. 295 



consisting in an alternation between the plant bearing sexual 

 organs (gametophyte) and the ascocarp (sporophyte). On germina- 

 tion the spores (ascospores) produced in the ascocarp give rise to 

 the sexual plant. 



2. The gametophyte produces gonidia but not on a special form {e.g. 

 Erysiphea?, Eurotiura, Penicillium). In these the gametophyte re- 

 produces itself by means of gonidia ; in the Erysipheoe and Euro- 

 tium the gametophyte generally produces sexual organs eventually, 

 that is, it generally becomes an actual gametophyte ; in Penicillium 

 the formation of sexual organs takes place only exceptionally 

 under special conditions, so that many successive generations of 

 potential gametophytes may be produced by means of gonidia 

 before an actual gametophyte makes its appearance. This may 

 occur also in the ErysipheuD. 



3. The gametophyte produces gonidia and is polymorphic. This 

 life-history can be clearly traced in Claviceps purpurea, the Ergot 

 of Rye. The mycelium is developed in the ovary of the Rye- 

 flower, and forms a continuous layer of hyphse, a compound gonid- 

 iophore, at the surface, from which immense numbers of gonidia 

 are formed by abstriction, imbedded in a mucilaginous substance 

 known as Honey-dew. This substance is eaten by insects, and 

 thus the gonidia are carried to other flowers and there reproduce 

 the fungus. This is the Sphacelia-form. When the rye is ripen- 

 ing, the mycelium forms a dense sclerotium (see p. 275), fusiform, 

 about an inch long, of a dark purple colour at the surface. This is 

 the Ergot, and it remains dormant until the following spring. On 

 germination the sclerotium gives rise to several filaments termed 

 stromata, about an inch long, each composed of a strand of hyphse, 

 which bear a swollen knob at their apices (Fig. 212). All over 

 the surface of the knob are a number of depressions, in each of 

 which there is an ascocarp (perithecium) containing a number of 

 asci, and in each ascus there are eight filiform ascospores. The 

 ascospores are carried by the wind to the Rye-flowers and there 

 give rise to the Sphacelia-form. A somewhat similar life-history 

 is that of Peziza Sclerotiorum, though the alternation of the two 

 forms of the gametophyte is not so regular : the asexual form of 

 the gametophyte (which corresponds to the Sphacelia-form of 

 Claviceps) bears simple gonidiophores and is known as Botrytis 

 cinerea. 



In some cases only gonidia-bearing forms are known (e.g. 



