3^4 



THALLOPHVTES. 



it is replciced 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 TuberaeeaB (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, Penicillium glaucum, is merely the conidia- 

 bearing mycelium of a small Truffle, has, however, thrown much light upon the 

 morphology of this group of Fungi. 



The mycelium of Penicillium glaucum grows upon nearly all organic substrata, even 

 upon liquids, forming a dense felt. From it erect filaments ai ise 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, Penicillium only produces its fructification when deprived of 

 air and of light, 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 affbrds 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 

 Penicillium has hitherto been known. 



' The sexual organs of Penicillium 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 poUinodium, 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. 



