3i6 



THALLOPHVTES. 



genous filaments; they give rise to asci and at the same time absorb the surrounding 

 sterile tissue. 



The dark colour of the interior of Truffles is due to the numerous dark-coloured spores, 

 and the marbled appearance with light and dark veins is the result of the distribution of 

 the bands of sporiferous filaments in the colourless sterile tissue. The latter contains 

 air between its hyphae and therefore appears white when seen by reflected light. The 

 spores of Truffles are formed in club-shaped or spherical asci of considerable 

 size, by a process of free-cell formation. They are invested by an exospore which is 

 covered with asperities, or has a rugose surface. 



It is as yet unknown whether or not the mycelium of the Truffles, like that of 

 PeniciUium, lives exposed to the air and forms conidia at any period of its existence. 



(5) The Pyrenomycetes^ usually produce their asci, which generally contain eight 

 spores and are of an elongated club-shape, within small flask-shaped or roundish recep- 

 tacles, which are termed perithecia. The wall of a free isolated perithecium (as in 

 Sphseria, Sordaria, and others) consists of a firm pseudoparenchymatous tissue of a dark 

 colour. The perithecium contains at first a delicate transparent tissue free from air, 

 which is afterwards absorbed by the asci and paraphyses. These spring from a hymenial 

 layer which clothes either the whole of the wall of the perithecium, or only its basal 

 portion. The perithecia are either open from the first (as in Sphceria typhina, Sordaria), 

 or they are originally closed and afterwards form an orifice clothed with hairs through 

 which the spores can escape {Xylaria). 



In a number of forms (Sphg&riae, simpUces such as Pleospora, Sordaria) the free 

 perithecia originate singly or in groups upon the inconspicuous filamentous mycelium 

 which usually inhabits dead plants, but occurs also on living ones. It is certain from 

 Woronin's observations upon Sphaeria Lemannex and Sordaria that in these cases each 

 perithecium is the result of a sexual act, and therefore represents an entire fruit. In 

 other Pyrenomycetes, however, a so-called stroma is first formed from the mycelium. 

 This is a cushion-shaped, mushroom-like, cup-shaped, or arborescent structure, consist- 

 ing of a dense mass of apparently homogeneous tissue, in which numerous perithecia are 

 developed. It remains uncertain whether, in such cases, the stroma is merely a peculiar 

 form of the mycelium within which the sexual organs are subsequently developed and 

 which bears a corresponding number of perithecia, or whether the entire stroma is the 

 result of one act of fertilisation and is therefore to be regarded as a single fructification 

 the asci of which are produced in numerous perithecia. Of these alternatives the latter 

 is the more probable, for in Claviceps the stroma itself is derived from a scelerotium, 

 which is doubtless the product of a sexual process. 



The asexual reproductive cells or conidia are developed, among the Pyrenomycetes, 

 not merely from the mycelium, but more especially from the stroma, and (as in Penicil- 

 Hum) even from the wall of the perithecium. They are formed on longer or shorter 

 hyphal branches usually in considerable numbers, and occasionally larger and smaller 

 conidia occur in the same species. It has already been pointed out that the receptacles 

 known as spermogonia and pycnidia"^, which also form larger and smaller conidia, are 

 probably parasites, and do not form part of the cycle of life of the plant which they 

 infest. 



I select as an example for more detailed description the Fungus which produces the 

 Ergot, — Clawceps purpurea^. Its development begins with the formation of a filamentous 



* Tulasne, Selecta fungorum carpologia, Paris 1860-65. — Woronin und De Bary, Beitrage zur 

 Morph. u. Physiol, der Pilze, Frankfurt 1870. — Fuisting, Bot. Zeitg. 1868, p. 179. [Gilkinet, Rech. 

 morph. sur les Pyrenomycetes, I, Sordariees, 1874.] 



^ [Bauke, Beitr. z. Kennt. der Pycniden, Nov. Act. Leop-Carol. Akad. 1876, has shown that, 

 in certain cases at least, the pycnidium with its stylogonidia is a definite part of the life-history of 

 these Fungi.] 



^ Tulasue, Anuales dcs Sci. Nat. vol. XX. p. 5. — Kiihn, Mittheilungen des landw. Inst, in Halle, 

 vol. I. 1S63. 



