3i6 
THALLOPHYTES. 
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 
Penicillium, 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 
Sphxria, 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 [Sphserix simplices 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 Sphseria Lemannese 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 Cla'viceps 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- 
lium) 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 sperrnogonia 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, — Cla'viceps purpurea^. Its development begins with the formation of a filamentous 
Tulasne, Selecta fungorum carpologia, Paris 1860-65. — Woronin und De Bary, Beiträge 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 pycnidiuna with its stylogonidia is a definite part of the life-history of 
these Fungi.] 
Tulasne, Annales des Sei. Nat. vol. XX, p. 5. — Kühn, Mittheilungen des landw. Inst, in Halle, 
vol. I. 1863. 
