FUNGI. CLEISTOCARPOUS ASCOMfCETES. 



107 



increase in size of the whole structure, fat perithecium. During the development of the 

 asci the filling-tissue becomes looser, its cells become round and capable of swelling, 

 lose their oily contents, and finally disappear; their place is occupied in the ripe 

 fructification by the eight-spored asci. As the perithecium increases in size the 

 cells of its walls enlarge and become covered with a sulphur-yellow coating which 

 acquires a considerable thickness and is formed probably of some resinous or fatty 

 substance ; they finally collapse and dry up. The asci disappear, and at length 

 the perithecium consists only of the brittle yellow covering and the mass of 

 spores, which it encloses, and a slight pressure is sufficient to release them. The 

 mycelium too, like the perithecium, is overlaid with a coloured substance, but in this 

 case it is of a chestnut colour, and the perithecia show on it as yellow granules 

 individually visible to the naked eye. The ripe spores have the form of biconvex lenses 

 (H) ; in germination the endosporium which developes the young germ-tube swells 

 strongly and bursts the exosporium in two halves. The mycelium produced by the 

 ascospores, like that which proceeds from the gonidia, gives rise first to gonidiophores 

 and then to perithecia ; but there is no true alternation between a sexual and an asexual 

 generation. 



c. The mycelium of Penicillium glaucum. grows on almost all organic substances, 

 even on fluids, on which it forms a dense felted covering. Erect branches rise from the 

 mycelium, which ramify in a penicillate manner and produce at their extremities long 

 chains of greenish gonidia, which are almost everywhere disseminated through the air 

 and account for the very general and spontaneous appearance of the Fungus. 



Penicillium forms its fructification only in the absence of air and light ; under these 

 conditions the tolerably conspicuous gonidiophores are not produced, and as the fructi- 

 fications are small yellowish bodies no larger than pins' heads, they were overlooked till 

 Brefeld succeeded in raising them by artificial cultivation. ' The mycelia 1 must be culti- 

 vated on a substratum, on which by help of abundant supplies of food and avoidance 

 of all disturbing causes it can reach its highest point of vegetative development. This 

 may happen in from seven to ten days from the sowing of the spores. Then suitable 

 methods must be adopted to hinder the access of atmospheric oxygen and the 

 consequent exhaustion of the mycelia by the production of gonidiophores. As these 

 conditions are not usually fulfilled in nature, it is no wonder that only the asexual 

 reproduction of Penicillium has hitherto been known. 



' The sexual organs of Penicillium agree in essential points with those with which 

 De Bary has made us acquainted in Eurotinm, and consist of a corkscrew-shaped 

 archicarp and an antheridial branch disposed in a similar manner with reference to the 

 archicarp. Here too the archicarp is closely invested with filaments which grow up from 

 beneath it ; but the archicarp itself grows at the same time and sends out branches 

 which make their way in among the filaments of the envelope. 



'When now an envelope of from eight to fifteen layers of filaments encloses the growing 

 archicarp, no new layers are formed, only there is some further development of the 

 old filaments. This consists chiefly in copious division of the filaments, and the cells thus 

 formed expand and close up into a tissue. This gradual formation of tissue at first impedes 

 and at last stops the advance of the ascogenous threads ; but they can be plainly seen 

 in a median section as stout hyphae arranged concentrically. During the formation of 

 this tissue the cells expand, but not uniformly, to six or eight times their previous size, and 



1 The account in the text is almost entirely taken from the 4th Ed., in which the preliminary 

 communication of Brefeld in Flora 1875 is printed word for word. A fuller account will be found in 

 his ' Schimmelpilze,' Heft II. Brefeld has since then come to the conclusion that the processes in the 

 formation of thesporocarp of Penicillium are not a sexual act, but a vegetative growth, and has even 

 applied this view to cases where, as in the Erysipheae, an archicarp and an antheridial branch are plainly 

 distinguishable. The homology of these organs however with similar ones in the Peronosporeae, 

 putting their function out of sight, may be considered as demonstrated by De Bary's recent researches ; 

 Penicillium, Peziza Sclerotiorum &c. are, as was stated above, retrograde forms. 



