158 THE AUSTRALIAN NATURALIST. 
The name is probably of Greek origin, derived from 
the word “‘Otlktos,’’? which means spotted, in allusion to 
the gibbi, cyphelle or pseudocyphellw, as the spots above 
referred to are technically called. 
During the past fifty years there has been a_ re- 
markable change in the classification of lichens, and much 
controversy owing to the dual nature of the plants, as 
it has been definitely proved that the general structure is 
composed of two distinct elements—a fungus and an 
alge. Some writers have advanced the theory that these 
compound organisms have entered into a mutual arrange- 
ment, which is termed symbiosis, or, in other words, a 
kind of consortism; while others contend that all hypo- 
theses of mutualism or consortism between the lichen 
and the symbiotic alga are erronous, and that the lichen 
is a fungus pure and simple. 
If we accept the latter view, it will be seen that the 
relation of the lichen—fungus to the lichen—alga is 
purely biological, and is of the utmost importance, as all 
plants are classified according to their fruits or repro- 
ductive organs, and that in the case of these plants, the 
systematic position in the vegetable kingdom depends 
upon the lichen-funeus. 
In a microscopic examination of the tissues of the 
thalius of stictacee it has been found that the chief 
families of the algal hosts, on which the lichen-forming 
fungi prey, are those commonly known as chlorophyll- 
green aigw, grouped under the family Palmellacex, and . 
the blue-green alg, grouped under the family Nostoc- 
cacew. Other races or families of algw, which have heen 
detected in the tissues of stictacem, are Protoecoecacer and 
Pleurococcacex. For example, in the section Ricasolia of 
the genus Lobaria, the algal or gonidial-layer of the 
thallus consists of Protococcus. In the section Knightiella 
of Lobaria, the algal-hosts are chiefly Csytococeus. Ta the 
section Lobarina, of the genus Lobaria, the algal-hosts are 
chiefly Polycoccus. ; 
On account of the difference of these algal-hosts, the 
lichens of the sections Ricasolia, Knightiella, and Loba- 
rina, have been raised to generic rank. 
In the same way, we find in the section Stictina, of 
the genus Sticta, blue-green algal-hosts, chiefly belonging 
to Polycoccus punctiformis, whereas in Sticta proper they 
