THE DUAL LICHEN HYPOTHESIS. 
103 
individuals in tlic ordinary sense of the word, they are rather 
colonies, which consist of hundreds and thousands of individuals, 
of which, however, one alone plays the master whilst the rest in 
perpetual captivity prepare the nutriment for themselves and their 
master. This master is a fungus of the class ascomycetes. a 
parasite which is accustomed to live upon other’s work, its slaves 
are green algae, which it has sought out, or indeed caught hold of, 
and compelled into its service. It surrounds them, as a spider its 
prey, with a fibrous net of narrow meshes, which is gradually con- 
verted into an impenetrable covering, but whilst the spider sucks 
its prey and leaves it dead, the fungus incites the algae found in 
its net to more rapid activity — nay, to more vigorous increase.”* 
In the volume “ Fungi ” in the International Scientific series, 
from page 10 to page 16, the theory in question is explained in a 
manner which I believe perfectly fair and just, with the principal 
objections to be urged against it. This was printed in 1875, but 
is still as applicable as it was then. Perhaps it errs in partaking 
too much of the character of a summary, and too little of an argu- 
ment. Had I not been challenged to give more distinctly the 
grounds of my opposition, that protest would have sufficed me. The 
hypothesis is thus briefly stated : — 
“ The two great points sought to be established are these, that 
what we call Lichens are compound organisms, not simple, inde- 
pendent vegetable entities ; and that this compound organism 
consists of unicellular algae, with a fungus parasitic upon them. 
The coloured gonidia which are found in tne substance or thallus 
of lichens, are the supposed Algse, and the cellular structure which 
surrounds, encloses, and imprisons the gonidia, is the parasitic fun- 
gus, which is parasitic on something infinitely smaller than itself, 
and which is entirely and absolutely isolated from all external in- 
fluences. ”| 
In plain words, the gonidia are algae, and all the rest of 
the plant is Fungus. At first sight it would appear that 
the whole controversy centered itself upon the definition of 
two words. A certain plant, with a peculiar organisation, has 
been hitherto by general consent represented by the term Lichen , 
whereas some modern writers contend that it should be called a 
Fungus , differing only from other Fungi in its power of enclosing 
certain unicellular algse within its substance. Shall these organ- 
isms still retain the name of Lichens , or shall they be called 
modified Fungi ? This is really one aspect which the hypothesis 
assumes, that of the value of two words. The theorists, on their 
part, maintain that it is something more than a mere definition of 
terms which is required, but they claim to have it accepted that 
Lichens (as they are called) are identical with Fungi (as commonly 
understood), but with the addition of certain extraneous bodies 
called “ gonidia,” which are truly microscopic Algae. 
* Schwendener, “ Die Algentypen der Flechtengonidien,” p. 3, 1869. 
t *‘ Fungi, their nature, use, ’ &c., pp. 11-12, 1875. 
