I 



CARPOSPORE.E. 329 



II. Green Algae. 



(6) Confervaceae {Cladophora) . . Ccenogonium, Cystocoleus. 



(7) Chroolepideae .... Graphideae, Verrucarieae, Roccella. 



(8) Palmellaceae .... Many fruticose and foliaceous Lichens. 



Cystococcus humicola . . Physcia, Cladonia, Evernia, Usnea, Bryopogon, 



and ylnaptychia. 

 Pleurococcus .... Endocarpon and various crustaceous 



Lichens. 

 Protococcus .... Cladonia, Physcia. 

 Stichccoccus . ... Sphccromphale, Polyblastia. 



(9) Coleochaeteae [Phyllactidium^ Kiltz.) Opegrapha filicina. 



The inconceivable opposition offered to Schwendener's theory by lichenologists 

 must surely be overcome by a recent publication of Bornet's\ After careful investi- 

 gation of sixty genera of Lichens, he comes to the conclusion that each lichen-gonidium 

 can be referred to some species of Algae, and that the relations of the hyphae to the 

 gonidia are of such a kind as to exclude any possibility of assuming the existence of 

 a genetic connection between them ; that they find, in fact, their only satisfactory 

 explanation in the theory of parasitism. Bornet shows that not only does the Alga 

 which is the host of the Fungus become modified in consequence of the cohabitation, but 

 that the Fungus itself often undergoes some change. He describes more accurately than 

 had previously been done how the hyphae of the Fungus attach themselves to the algal 

 cells, and even penetrate into them, in order to absorb their contents, as the occurrence 

 of the empty cell-walls of gonidia in the lichen-thallus suggests. He did not content 

 himself with seeking in nature material which would show the Algae being attacked by 

 the lichen-fungus and the gradual formation of the thallus, but he sow^ed spores of Lichen- 

 fungi upon Algae "^ in order to be able to observe the manner in which the Fungus avails 

 itself of the Alga. Of more especial interest is his proof of the fact that the same Alga 

 may serve for very different Fungi; for example, Chroolepus umbrinum supports no less 

 than thirteen genera belonging to five families of Lichens. Although many Lichen-fungi 

 require to have particular Algae as their hosts, a condition which occurs also in other cases of 

 parasitism, it also happens that the same Lichen-fungus can avail itself of various forms 

 of Algae as its gonidia. The Alga which has been attacked by the Fungus and has 

 become surrounded by its hyphae is not always hindered in its growth, but in many 

 cases is actually stimulated to more active vegetation. For further important details 

 I must refer the reader to the work itself. 



All reliable observations thus lead to the conclusion that a lichen-thallus is a mycelium 

 which is nourished as a parasite by an Alga. The fructification of the Lichen, the 

 apothecium or perithecium, belongs exclusively to the mycelium. 



[The most conclusive evidence in favour of the truth of Schwendener's theory has 

 been brought to light by the researches of StahP. In the first place, he succeeded, by 

 cultivating the spores and hymenial gonidia of Endocarpon pusillum, in producing arti- 

 ficially a Lichen-thallus which bore perithecia and spermogonia. In the second place, 

 he discovered that carpogonia are present in the thallus of certain Lichens which he 

 investigated. The carpogonium of Collema microphylliim, for instance, is a hyphal 

 filament which forms closely appressed coils at some distance below the surface of the 

 thallus, and is then prolonged straight to the surface beyond which it projects. The 

 carpogonium thus consists of two parts, the coiled portion, which Stahl terms the asco- 

 gonium, and the straight portion, which he calls the trichogyne. Spermatia, derived from 



^ Bornet, Recherches sur les Gonidies des Lichens, Ann. des Sci. Nat. t. XVII. 1873. 



^ Compare also Reess, Monatsber. der Berl. Akad. 1871 ; and Schwendener, Flora, 1872; also 

 Treub, Bot. Zeitg. 1873. 



2 [Beitrage zur Entwickelungs-geschichte der Flechten, I, IT, 1877: also de Bary, Die Ev- 

 scheinung der Symbiose, 1879.] 



