120 
THE DUAL LICHEN HYPOTHESIS. 
Our experience of fire, in whatever form it occurs, is that it 
burns or consumes that upon which it operates. We have no ex- 
perience of fire which does not support itself by causing that 
change of form and condition which we term combustion. Hence 
we are justified by experience in rejecting any theory based upon a 
reversion of this fact, that is, on the assumption that fire does not 
consume. 
Inasmuch as the supposed fungus, said to be parasitic upon the 
gonidia, does not “ destroy its host plant, in the unequal struggle,” 
it cannot be a fungus, since, if it were a fungus, the gonidia would 
be destroyed, as demonstrated by experience. Or , if it were proven 
to be a fungus, then, not being parasitic, the gonidia are not foreign 
to it, but a portion of its substance; and again a dilemma occurs, 
for no fungus is known persistently to enclose green granules. 
Relative size is another strong presumption against parasitism. 
In the Lichen we have a supposed parasite many times larger than 
its host. It is an elephant parasitic upon a flea, and not a flea upon 
an elephant. The parasite in the romance encloses and cherishes 
its host, which is buried within its substance, reminding one strongly 
of an entozoon, enclosed in the body of an animal, horse, dog or 
man. In such a case it is not usual to call the man or the animal 
the parasite, and the entozoon the host, but the reverse. If it is 
urged that this is not an analogy, because the entozoon is known to 
subsist upon the animal in which it is found, then, in like manner 
I would urge that it is not proved that the gonidia do not subsist 
at the expense of the so-called fungus. In other w r ords, it is 
more feasible to suppose that the assumed green algae are parasitic 
than that they should be the host. 
Again, if it can be shown that gonidia are part of the whole 
plant, they cannot be distinct from the plant. If they are pro- 
duced by the healthy and normal action of the plant, then they are 
attributes of the plant. If they are beneficial to the plant, acting 
as organs, performing useful functions, then there is no more para- 
sitism than in the leaves of an oak or the tendrils of a vine. 
It is needless to recapitulate what has already been alleged that 
the gonidia are generated by the plant itself, and hence there can 
be no parasitism. 
Dr. Nylander writes : “ The absurdity of such an hypothesis is 
evident from the very consideration that it cannot be the case that 
an organ (gonidia) should at the same time be a parasite on the 
body of which it exercises vital functions ; for with equal propriety 
it might be contended that the liver or spleen constitutes parasites 
of the mammiferse. Parasitic existence is autonomous, living upon 
a foreign body, of which nature prohibits it from being at the same 
time an organ.”* 
All conclusions as to the general character of Lichens, based 
upon experiences of the Collemaceas, are essentially unsatisfactory. 
* “ Grevillea” ii, p. 146. 
