3H 
THALLOPHYTES. 
it is replaced by the asci. The increase in size of the cells of the parietal layer keeps 
pace with that of the whole perithecium, and they become covered with a sulphur- 
yellow coating which attains a considerable thickness and consists probably of a resinous 
or fatty substance. Finally these cells also collapse and dry up ; the eight-spored asci 
also break up, till finally the perithecium consists only of the brittle yellow coating and 
of the mass of spores enclosed by it, which are set free by gentle pressure. In a 
similar manner to the perithecium, the mycelium also becomes covered by a coating, 
in this case of a chestnut colour, on which the perithecia are now individually visible 
to the naked eye as yellow granules. The ripe spores have the form of biconvex lenses 
{H) ; when germinating the endospore which puts out the germinating filament swells 
up violently and splits the exospore into two halves. The mycelium which proceeds 
from the ascospores produces, like that which arises from the conidia, at first conidio- 
phores and afterwards perithecia ; but a proper alternation of sexual and non-sexual 
generations does not occur here. 
(4) The Tuberaeese (Truffles) form subterranean tuberous fructifications, which 
may be as large as a clenched fist. They are usually provided with a firm thick 
cortex of pseudo-parenchyma, and consist internally of a dense felt of hyphae in 
which the ascogenous filaments ramify. The asci, within which the spores are pro- 
duced, are imbedded in this tissue, and are arranged in groups or layers of various 
forms which, in a section, present the appearance of chambers or of a dark veining. 
Until recently the development of these fructifications had not been traced, and their 
morphological structure was but imperfectly understood. The discovery made by 
Brefeld that the commonest of all Moulds, Penic'iUium glaucum, is merely the conidia- 
bearing mycelium of a small Truffle, has, hovi'ever, thrown much light upon the 
morphology of this group of Fungi. 
The mycelium of Penictllium glaucum grows upon nearly all organic substrata, even 
upon liquids, forming a dense felt. From it erect filaments arise which form at their 
upper ends pencils of branches, and at the extremities of these long rows of greenish 
conidia are developed. These conidia are everywhere dispersed in the air, and it is for 
this reason that this Fungus is of such universal occurrence. 
Like the Truffles, PeniciUium only produces its fructification when deprived of 
air and of fight, under circumstances in fact which are unfavourable to the develop- 
ment of the conidiophores. The fructifications are of a yellowish colour and attain the 
size of a small pin's head. On this account they were overlooked until Brefeld suc- 
ceeded in producing them artificially. ' The mycelium ^ must be cultivated upon a 
substratum which aff'ords it abundant nourishment and enables it to attain, without any 
interruption, its most complete vegetative development. This is reached as a rule 
in from seven to ten days after the spores have been sown. The access of the atmo* 
spheric oxygen must now be diminished by proper means, and the exhaustive formation 
of conidiophores will thereby be prevented. Since these conditions are not commonly 
fulfilled in nature, it is easy to understand why it is that only the asexual form of 
PeniciUium has hitherto been known. 
' The sexual organs of PeniciUium agree in all essentials with those of Eurotium 
described by De Bary. They consist of a spirally-wound ascogonium (carpogonium), 
the female organ, and of a pollinodium, the male organ. 
' After the fertilisation of the ascogonium, a process of development commences 
which difi'ers very materially from anything of the kind as yet described among 
the Ascomycetes. In this case also the fertilised ascogonium becomes invested by 
filaments which arise, evidently in consequence of fertilisation, from beneath the 
ascogonium, but here the ascogonium itself at once begins to grow and its branches 
extend among the surrounding filaments. When the growing ascogonium is enclosed 
by eight or more (8-15) layers of filaments, no new layers are formed, but those which 
^ The following is taken literally from Brefeld's preliminary account in Flora, 1873^ no. 21. . 
