108 FIRST GROUP. THALLOPHYTES. 



finally their cell-walls become much thickened. This thickening begins simultaneously 

 at two points, inside in the ascogenous hyphae, and outside in a zone which lies some cell- 

 layers deep beneath the periphery. 



' The fructification, which is now detached from the mycelium and is of the size and 

 colour of a coarse yellow grain of sand, is in this state a sclerotium ; the outer surface is 

 composed of from two to four layers of cells which are longer in the tangential direction 

 and of a yellow-brown colour. These are followed by large cells more radially dis- 

 posed, which diminish in size from without inwards, and are traversed by stiff asco- 

 genous hyphae disposed in the tissue and looking like much-branched passages. 



'The sclerotium if kept dry will go through a resting stage of more than three months 

 without losing the power of germination, but if it is placed on damp blotting paper, 

 a further development of the ascogenous hyphae takes place after a period of from six 

 to seven weeks ; they again assume the appearance of living hyphae and divide into 

 short cells, and each cell can produce a shoot which divides at once into a thick and a thin 

 filament. The thick filaments have to do with the formation of the fructification, the thin 

 ones consume the surrounding tissue and supply food to the thick ones. The thin filaments 

 are less branched and have no partition-walls ; the thick ones form numerous lateral 

 branches closely following one another just beneath their apex, and have a septum 

 between every two branches. These branches form a continuous chain of asci, and 

 each ascus forms eight spores. The further development concludes with the absorption 

 of all the tissue inside the brown envelope ; the ripe asci, the hyphae from which they 

 sprang, and the filaments that supplied them with food disappear ; and finally, after 

 a period of from six to eight months, the sclerotium, though not changed in outward 

 appearance, is only a vesicle containing a dense mass of countless bright-yellow 

 spores. 



' Each ascospore under proper cultivation developes a mycelium, which is in every 

 respect the same as that produced from a gonidium and is marked out by the very charac- 

 teristic gonidiophore ; the origin of each gonidiophore can be traced back through the 

 mycelial filaments to a single spore. 



'" If the sclerotium loses the power of germination through being too much dried or 

 through age or other disturbing causes, that is, if the ascogenous filaments inside it 

 are dead, single cells of the tissue will sometimes germinate. The germ-tubes protrude 

 through fissures in the sclerotium and produce the usual gonidiophores on its surface. 

 Here the physiological distinction, or rather the contrast between the ascogenous 

 filaments and the tissue that surrounds them, is still more clearly shown." 



3. The PYBENOMYCETES J produce their long club-shaped asci, which usually 

 contain eight spores, inside small roundish or flask-shaped receptacles known as 

 peritheda ; the outer covering of the perithecium, especially when it is free and isolated, 

 as in Sphaeria and Sordaria and others, is composed of a firm tissue of pseudo-paren- 

 chyma which is usually of a dark colour. Inside this there is in its early state a deli- 

 cate transparent tissue containing no air, which is eventually supplanted by the asci 

 and paraphyses ; these have their origin in a hymenium which lines the wall of the 

 perithecium or occupies its base only. The perithecium is either open from the first, as 

 in Sphaeria typhina and Sordaria^ or it is at first closed and afterwards forms a canal- 

 like aperture clothed with hairs through which the spores escape, as in Xylaria. 



In a number of species (the Sphaeriae simplices, such as Pleospora and Sordaria) 

 the free perithecia grow singly or in groups on the inconspicuous filamentous mycelium, 



1 Tulasne, Selecta fungorum carpologia, Paris, 1860-65. Woronin u. De Bary, Beitr. z. Morph. 

 u. Phys. d. Pilze, Frankfurt 1870, [and De Bary, Morph. sc. d. Pilze, 1884, p. 200], Fuisting 

 in Bot. Zeit. 1868, p. 179. Bauke, Beitr. z. Kenntn. d. Pycniden (Nova Acta Leop. Car. 1876). 

 Bauke, Zur Entwicklungsges. d. Ascomyceten (Bot. Zeit. 1877). Zopf, Die Gonidienfriichte von 

 Fumago (Nova Acta Leop. Car. 1879) > [Id. Zur Kenntn. d. anatom. Anpass. d. Pilzfruchte an die 

 Funktion der Sporenentleerung. Halle, 1884.] 



