CARPOSPORE.E. 
3^9 
II. Green Algae. 
(6) Confervaceae {Cladophora) . . Cmnogonium, Cystocoleus. 
(7) Chroolepideac .... Graphideae, Verrucarieae, Roccella. 
(8) Palmellacese .... Many fruticose and foliaceous Lichens. 
Cystococcus humicola . . Physcia, Cladonia, Evernia, Usnea, Bryopogon, 
and Aiiaptychia. 
Pleurococcus .... Endocarpon and various crustaceous 
Lichens. 
Protococcus .... Cladonia, Physcia. 
Stichccoccus . ... Sphccromphale, Polyblastia. 
(9) Coleochaeteae [Phyllactidium, Kütz.) 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-gonidiuni 
can be referred to some species of Algse, and that the relations of the hyphs 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 algai 
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 hchen-fungus and the gradual formation of the thallus, but he sowed 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, Cbroolepus imibrinum 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 Stahl In the first place, he succeeded, by 
cultivating the spores and hymenial gonidia of E?idocarpon 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 microphyllum, for instance, is a hyphal 
filament which forms closely appressed coils at som.e 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, whi'ch he calls the trichogyne. Spermatia, derived from 
' Bornet, Recherches sur les Gonidies des Lichens, Ann. des Sei. Nat. t. XVII. 1873. 
^ Compare also Reess, Monatsber. der Berl. Akad. 1871 ; and Schwendener, Flora, 1872 ; also 
Treub, Bot. Zeitg. 1873. 
^ [Beiträge zur Entwickelungs-geschichte der Flechten, I, II, 1877: also de Bary, Die Ei- 
scheinung der Symbiose, 1879.] 
