INTRODUCTION, 



339 



mycete, of which a diagrammatic section is given in F. w is the carpogonium 

 consisting of several cells, which is fertilised by the tubular branched pollinodium ; 

 the result is that a number of filaments shoot out from a central cell of the" 

 carpogonium, which then form sacs at the apices of their branches, and in these 

 a number of carpospores. The envelope of the sporocarp is in this case very 

 massive, and consists of cellular filaments which shoot out beneath the carpogonium ; 

 and it finally forms a compact pseudo-parenchyma in which the carpogonium is en- 

 closed together with the ascogenous filaments and the asci which proceed from them. 

 The mycelium which produces the carpogonia in both the Fungi now described is 

 inconsiderable in comparison to the large sporocarp which results from the fer- 

 tilisation of the carpogonium ; the sporocarp itself in many cases continues to grow 

 for some time independently of the mycelium, and therefore constitutes a second 

 (non-sexual) generation of these Fungi. If the mycelium were large and vigorous, 

 and the sporocarp which springs from it small, as is the case in the Florideae and 

 Characeae, the sporocarp would in these cases also have the appearance of being 

 only an appendage of the sexual generation, and an alternation of generations 

 would scarcely •be suggested, although this does actually occur, since the entire 

 course of development of such a Fungus can be divided into two sharply-defined 

 phases, of which the first is the mycelium with its sexual organs, while the second 

 is the sporocarp with its independent power of growth. 



Besides the true spores produced directly or indirectly by the act of fertilisation, 

 which complete the course of development of the plant by a rudimentary or an 

 evident alternation of generations, there is commonly among Thallophytes an 

 extremely productive propagation by gonidia which are not brought into existence 

 either directly or indirectly by any act of fertilisation, and which have therefore 

 nothing to do with the alternation of generations. 



The Gonidia^ often arise on the thallus by the whole of the contents of 

 certain cells of the thallus dividing, and thus producing one or more gonidia 

 which become detached from the plant. But in other cases special supports or 

 receptacles are formed on the thallus, the sole function of which is to produce 

 gonidia, either by the abstriction of the ends of special branches {Siylogonidm, as 

 in Ptpfocephalis, Pemcillium, &c.), or by free cell-formation in the interior of large 

 cells (Undogom'dia, as in the Saprolegnieae, Mucorini, and Vaucherid). In many 

 cases, especially among Fungi, propagation is effected almost exclusively by such 

 gonidia, the normal completion of the development by actual fertilisation being 

 attained only under specially favourable conditions. This is the reason why the 

 sexual organs of many Thallophytes are at present entirely unknown, while their 

 gonidia are perfectly familiar. It is therefore often a very difficult matter to 

 assert with respect to a Thallophyte, that it never produces sexual organs; since 

 even in the case of the common Mould-fungus {Penicilliuni) and in many Algae, 

 the gonidia of which have long been known, it is only quite recently that the sexual 

 organs and the alternate generation resulting from them have been discovered. Even 

 in the majority of the large marine Algae, the Phseosporeae, and the numberless 



^ Among Fungi the small gonidia which become detached in great numbers are also calltd 

 Conidia, from the Greek Kovia^ dust. 



