322 THE MICROSCOPE AND ITS REVELATIONS. 



der the filtered air t( optically pure/' by passing it through cotton wool, 

 or may be got rid of by allowing them, time to subside in a closed cham- 

 ber whose bottom is smeared with glycerine, so that they are held down 

 when once they have settled on it. 



318. This mode of explanation has received further confirmation from 

 the facts recently ascertained, in regard to the great number of forms 

 under which a single germ may develop itself. For it. has been ascer- 

 tained with regard to the Fungi generally, that different individuals of 

 the same species may hot only develop themselves in very dissimilar 

 modes, but may even bear dissimilar types of fructification; and further, 

 that even the same individual may put forth, at different periods of its 

 life, those two kinds x>f fructification the Basidio-sporous, in which 

 spores are developed by outgrowth from free points (fastdia), and the 

 Ascomycetous, in which they are developed in the interior of cases (tliecm 

 or asci, Fig. 205) which had been previously considered as separately 

 characterizing the two principal groups into which the Class was prima- 

 rily divided. But the spores produced from the ostensible ' fructifica- 

 tion ' in this Class are all non-sexual or gonidial ( 228). In a large pro- 

 portion of it, nothing whatever is known of the true Generative process; 

 and wherever it has been detected, it is performed in a manner that car- 

 ries us back to the simplicity of the lower Algal types. Thus the myce- 

 lium of the common Mucor which forms the ' brown mould' of bread, 

 preserves, etc., consists of a single cell, which first sends forth wide- 

 spreading branches that extend over the surface on which it grows, and 

 then develops a vertical pin-like stem, enlarging at its top a little globu- 

 lar ( head,' the cavity of which is cut off from that of the stem by a par- 

 tition, so as to form a separate * sporangial ' cell, whose endoplasm breaks 

 up into a number of * micro-gonidia;' and every one of these, when set 

 free by the bursting of the sporangium, can give origin to a new myce- 

 lium. But the Generative act is performed in the mycelium itself; two 

 branches of which, coming into contact with each other at their free ex- 

 tremities, there form separate terminal cells, the fusion of which unites 

 their two endoplasms into one (just as in the conjugation of Mesocarpus, 

 235); and this, surrounding itself with a thick cell-wall, becomes aa 

 ' oospore,' which may remain a long time in the dry state without germi- 

 nating. It is by the formation of gonidia that a e mould ' whose germ 

 has fallen upon a fruitful soil rapidly extends itself over a large surface; 

 whilst the carrying of the oospores by currents of air forms the chief 

 means of its transmission to a distance. The Penicillium, or 'green 

 mould,' on the other hand, sends-up from its mycelium a branching 

 stem, the ramifications of which subdivide into a brush-like tuft of fila- 

 ments, each of which bears at its extremity a succession of minute 

 * beads ' termed conidia. These, detaching themselves and falling on a 

 suitable soil, forthwith germinate into new mycelia; or, drying up, are 

 disseminated by atmospheric currents, without loss of their vitality. 

 Here, again, the Generative act is performed in the mycelium: bnt by a 

 somewhat more complex apparatus than in Mucor. One of its branches 

 elongates, and coils spirally upon itself into a corkscrew-like body, the 

 ascogonium, which constitutes the female organ; whilst another branch 

 acts as the male organ, the pollinodium* which 'extends itself over the 

 spire, and communicates to its endoplasm some fertilizing material from 

 its own. The germ thus formed becomes inclosed in a mass of sterile tis- 

 sue; and within this it develops itself into a cluster of asci, each contain- 

 ing numerous spores, whose liberation gives origin to a ( new generation.' 



