Recent Works on Lichens. A. Lorrain Smith. 195 
In the lime lichens associated with Tventepohlia there is also 
contact without penetration, and free wandering gonidia are 
frequent ; in those associated with Protococcaceae there is a well- 
marked zone of gonidia and in certain species occur wandering 
members unconnected with hyphae. 
He found, however, true parasitism in the thallus of Avrtho- 
pyrema tichothecioides: the gonidia (Gloeocapsa sect. Xantho- 
capsa) form a poorly developed layer towards the surface of the 
thallus; no wanderers occur in the deeper tissue. The hyphae 
form a circle round the algal cells which is never quite complete ; 
the swollen ends of the hyphae act as haustoria and destroy 
some of the algae. This unusual and peculiar habit of growth 
has induced him to place the species in a new genus, Xantho- 
pyrema. It may also be noted that a blue-green gonidium in 
Arthopyrenia is exceptional. 
Bioret (1921) also noted a case of parasitism in the thallus of 
Opegrapha herpetica which has very large gonidial cells (Tvente- 
pohlia). In several instances he observed penetration of these 
gonidia by haustoria of the hyphae—the only instances recorded 
of parasitism in Graphidaceae. Bioret evidently found parasi- 
tized gonidia in only one individual of the species. 
An undoubted case of parasitism is brought forward by 
Goebel (1915). He describes a species of Ephebe from an aqueous 
habitat in Brazil. The alga—St:gonema—was destroyed by the 
penetrating haustoria of the fungus hyphae, more particularly 
in the centre of the thallus. The gonidia towards the periphery 
were less seriously attacked, and those at the growing tips were 
practically undamaged. This parasitic condition is not charac- 
teristic of our native Ephebes which inhabit a more or less dry 
substratum. 
McWhorter (1921) adduces as proof of the parasitic nature of 
lichens—or more particularly of lichen hyphae—the cases he 
has observed in which mosses are destroyed by lichens— 
Cladoniae, Physciae, Amphiloma etc. The destruction was partly 
due to parasitism and partly to smothering. He thus finds con- 
firmed Bruce Fink’s definition: “‘a lichen is a fungus which lives 
during all or part of its life in parasitic relation with an algal 
host and also sustains a relation with an organic or inorganic 
substratum.”’ His work however proves nothing in regard to 
the algal host, though the relation to the organic substratum is 
evidently that of a marauder. 
M. and Madame Moreau (1921) have their own views as to 
the problem of symbiosis: they look on the lichen—the fungal 
part—as a gall-structure due to the exciting action of the alga. 
They have studied the occurrence of cephalodia in Solovina and 
find in their structure new proof of the gall-theory. All the 
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