124 
THE DUAL LICHEN HYPOTHESIS. 
enclosed in cup-shape receptacles, so have certain Lichens, ergo, 
Lichens are Fungi. But lichens enclose in their thallus green 
bodies not found in Fungi, hence the Lichens are Fungi, enclosing 
green bodies which are foreign to it. There must be something 
wrong somewhere, what are these round, unicellular, greenish, free 
vesicles. Some of the unicellular Algae consist of round, unicel- 
lular, greenish, free vesicles. Ergo, these gonidia are algae. There 
must be parasitism somewhere with a Fungus, and a Lichen in the 
same plant, and thus the dual Lichen hypothesis is ushered upon 
the world, based on a tissue of analogies, mistaken for identities. 
How aptly may an observation, made by Professor Huxley, when 
considering another hypothesis, be applied here : “ In a scientific 
enquiry a fallacy, great or small, is always of importance, and is 
sure to be, in the long run, constantly productive of mischievous, 
if not fatal results.”* 
It is, undoubtedly, a fallacy to assume that things which are 
only analogous are identical, as if there were no real difference 
between analogy and identity. In the present instance no more 
decided evidence need be given than in the case of the gonidia. It 
has been deemed unnecessary to demonstrate that they are Algae, 
but simply on the faith of their analogy has identity been assumed. 
The interests of truth demand that fallacies should be encountered, 
and not accepted on the faith of any authority whatever, be that 
authority ever so great, or ever so highly esteemed amongst men. 
Broken-down theories are, by no means, unknown in the Annals of 
Science, and the addition of another will create no great surprise. 
Some may remember the elaborate treatise of Professor Mene- 
ghini, in 1845, translated for the Kay Society in 185*3, in which 
he essayed to prove the animal nature of Diatoms, a theory which 
at once found adherents, and it came nigh to being pronounced one 
of the great discoveries of science, and yet no one believes it now. 
Or even the more recent theory of spontaneous generation, sup- 
ported by the overwhelming evidence of the experiments of M. 
Pouchet. Yet the evidence and the theory collapsed, thanks to the 
indomitable perseverance of M. Pasteur, but not before it had 
acquired many adherents, and even in England scientific journals, 
of no small repute, announced it as one of the great discoveries of 
the age 
And not many years since the theory of the animal nature of 
the Myxogasters obtained the support of some botanists and many 
zoologists, although the mycologists generally declined to accept it. 
Perseverance has established the fallacy of the theory, but the 
lesson it suggests is evident, when we remember that the same 
individual who propounded that theory was the first to announce and 
propose the Algo-lichen hypothesis, which was taken up by Scliwen- 
dener and afterwards by Bornet. A third proposition from the 
same source died without a fiiend. 
* Huxley, “ Lectures ” (1863), Hardwicke, pp. 67. 
