330 THA LL OPHYTES. 



the spcrmogonia, are disseminated over the surface of the thallus by the agency of water, 

 and are thus brought into contact with the projecting cell of each trichogyne, and to this 

 they adhere. The contents of one at least of the spermatia pass into the trichogyne in 

 consequence of the absorption of the cell-walls at the point of contact, and thus the 

 carpogonium is fertilised. It will be seen that this mode of fertilisation is the same as 

 that which has been described in the case of the Florideae. In consequence of fertilisa- 

 tion the cells of the ascogonium, as well as those of the adjacent hyphae, are stimulated 

 to growth, and the result is the formation of an apothecium ; from the ascogonium are 

 produced the asci, and from the adjacent hyphae the paraphyses and the wall. It is clearly 

 shown that the apothecium is derived solely from the fungal constituent of the Lichen. 

 These results, besides throwing light upon the nature of Lichens, give a clue to the 

 significance of the spermogonia and spermatia in other Ascomycetes and in the iEcidio- 

 mycetes.] 



B. The ^cidiomycetes \ 

 {UredinecE.) 



If, in characterising this group, attention is confined, as in the case of the 

 preceding groups, to those forms whose development is completely known, two 

 extreme cases, as regard the conditions of reproduction and the alternation of 

 generations, present themselves. In the simplest case the mycelium produces 

 a fructification, the so-called JEcidium, which consists, in its mature condition, of 

 a cup-shaped investment {peridmm) and of a hymenium occupying its basal part; 

 from the basidia of the hymenium spores are formed by abstriction. The spores 

 thus produced {cBcidiospores) at once germinate, and each one developes a short fila- 

 ment consisting of but few segments, the growth of which soon ceases, and bearing 

 upon short delicate branches smaller reproductive cells, the sporidia, which may be 

 included under the term conidia in the sense in which that term has hitherto been 

 used. The hypha bearing them is to be regarded as a promycelium. The sporidia, 

 on germination, throw out hyphae which penetrate into the epidermal cells of the 

 host, and give rise to a mycelium which, in its turn, forms aecidium-fruits. In this 

 case, which is found represented by Endophyllum Sempervivi, there occurs a simple 

 alternation of generations, the alternating generations being the mycelium and the 

 fructification (secidium), with the slight variation that the aecidiospores give rise to 

 the mycelium not directly but indirectly by means of the promycelium and its 

 sporidia. The other extreme case is represented by jEcidium Berbertdis, ^cidiuni 

 Leguminosarum, and others. Here new mycelia are directly formed by the secidio- 

 spores, without the intercalation of a promycelium. They do not, however, give rise 

 to aecidium-fruits but develope conidia (the so-called Uredospores) upon basidia closely 

 packed so as to form a kind of cushion, by means of which numerous generations 

 of mycelia are produced during the period of vegetation. It is not until later that 

 reproductive cells of another kind, the Teleutospores, are produced in these genera- 

 tions to which the name Uredo has been given. These germinate in the following 



^ Tulasne, Ann. des Sci. Nat. 3rd ser, vol. VII; 4th ser. vol. II. — De Bary, Ann. des 

 Sci. Nat. 4th ser. vol. XX, and Monatsber. d. Berl. Acad. 1865. — Oersted, Bot. Zeit. 1865. p. 291. — 

 Reess, Die Rostpilzformen der devitschen Coniferen, Halle 1869 (Abh. der naturf. Gesellsch. Bd. XI). 

 • — Oersted's System der Pilze, Lichenen, iind Algen, translated into German by Grisebach and Rcinke, 

 Leipzig 1873, p. 19. [Schroter, Entwick, einig. Rostpilze, in Cohn's Beitrage, I, 1875.] 



