328 
THALLOPHYTES. 
while the soredia are still included in the mother-thallus ; soredial branches, as they are 
termed, are thus produced. 
We may now turn to the consideration of the other elemental form out of which, in 
addition to the Fungus-hyphae, the thallus of Lichens is constructed, the Gon'idta. It has 
already been suggested that these are nothing but Algae which are attacked and sur- 
rounded in their growth by Ascomycetes, and serve as hosts to them, the capability of 
assimilating inorganic materials being wanting on the part of their parasites. 
Passing over the views of the older lichenologists, which will be found collated in the 
writings, cited below, of Baranetzky and of Schwendener, it may be pointed out here that 
De Bary (Handbuch der physiol. Bot. vol. ii. p. 291) arrived at the following alternative 
conclusions with respect to the gelatinous Lichens, such as Ephehe and similar forms ; 'that 
either these Lichens are the completely developed fructifying states of plants the 
incompletely developed forms of which have hitherto been placed among Algae, as 
Nostocaceae and Chroococcaceae, or the Nostocaceae and Chroococcaceae are typical Algae 
which assume the form of Collemae and Ephebae &c., in consequence of the penetration 
into them of certain parasitic Ascomycetes the mycelium of which extends throughout the 
growing thallus and often becomes attached to the cells filled with phycochrome 
{Plectospora, Omphalaria). In the latter case the plants in question might be termed 
Pseudolichens,' From the close of this quotation it appears that the writer does not 
apply the latter alternative to the heteromerous Lichens at any rate. Soon afterwards 
Famintzin and Baranetzky, and then the latter alone, published researches upon the 
further changes which the gonidia of Lichens undergo when they are set free by the 
decomposition of the hyphal tissue in water ^ Baranetzky comes to the conclusion that 
' the gonidia of the heteromerous chlorophyll-containing Lichens {Physcia, E'vernia, Cla- 
donia), as well as the heteromerous forms containing phycochrome {Peltigera) and of the 
gelatinous Lichens (Col/ema), are capable of carrying on an entirely independent life out- 
side the lichen-thallus. When set free, the lichen-gonidia appear to extend their cycle of 
life; thus, for instance, the independently vegetating gonidia of Physcia, E'verma, and Cla- 
donia produce zoogonidia.' He also found that all the cells of the spherical masses com- 
posed of the gonidia of Peltigera undergo a transformation so as to become extremely like 
the interstitial cells of a Nostoc, and he did not doubt that this was their permanent 
condition. 'Some, perhaps many, of the forms hitherto described as Algae must be considered 
as independently vegetating lichen-gonidia, for the present at any rate ; such are Cystococcus, 
Polycoccus and Nostoc.'' The researches of Schwendener carried on, in part earlier, in part 
simultaneously and later, in the most careful manner, led to the opposite conclusion, that 
the gonidia are in fact Algae which are more or less disturbed in their manner of life by 
the Fungus which is parasitic upon them. He first definitely stated and explained this 
view in his treatise ' Ueber die Algentypen der Flechtengonidien,' (Basel, 1869), as 
applying to all Lichens. In this memorable work, which assigned to the Lichens for the 
future their true systematic position among the Ascomycetes, he gives an account of those 
genera of Algae which were to that time known as the hosts of lichen-fungi, that is, as 
playing the part of gonidia. 
I. Bluish-green Algae. (Nostochineae.) 
Name of group of Alga. Lichen in ^vhich they occur as gcnidia. 
(1) Sirosiphonese . . Ephebe^ Spilonema, Polychidium. 
(2) Rivularieae . . Thamnidium, Lichina, Racobletina. 
(3) Scytonemeae . . Heppia, Porocyphus. 
(4) Nostocaceae . . CoUema, Lempholemma, Leptogium, Pannaria, Peltigera. 
(5) Chroococcaceae . . Omphalaria, Euchylium, Phylliscium. 
1 Mem. de I'Acad, Imp. des Sei. de St. Petersbourg, 7th series, vol. XI. no. 9. and Melanges 
biologiques tires du Bulletin de I'Acad. Imp. de St. Petersbourg, vol. VI. 1867. — [Ann. des Sei. Nat. 
5th series, 1867, vol. VIII. pp. 1 37-144.] — Also Itzigssohn, Bot. Zeitg. 1868, [and Woronin, Ann. Sei. 
Nat. XVL 1872]. 
