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xxiv INTRODUCTION
In the absence of any " visible " seed, there was much speculation in
early days as to the genesis of all the lower plants and many opinions
were hazarded as to their origin.
1
, Luyken for instance, thought that lichens
were compounded of air and moisture. Hornschuch 2 traced their origin to
a vegetable infusorium, Monas Lens, which became transformed to green
matter and was further developed by the continued action of light and air,
not only to lichens, but to algae and mosses, the type of plant finally evolved
being determined by the varying atmospheric influences along
with the
chemical nature of the substratum. An account 3 is published of Nees von
Esenbeck, on a botanical excursion, pointing out to his students the green
substance, Lepraria botryoides, which covered the lower reaches of walls and
rocks, while higher up it assumed the grey lichen hue. This afforded him
sufficient proof that the green matter in that dry situation changed to
lichens, just as in water it changed to algae. An adverse criticism by
Dillenius 4 on a description of a lichen fructification is not inappropriate to
"
those early theorists : Ex quo apparet, quantum videre possint homines,
si imaginatione polleant."
A constant subject of speculation and of controversy was the origin of
the green cells, so dissimilar to the general texture of the thallus. It was
thought finally to have been established beyond dispute that they were
formed directly from the colourless hyphae and, as a corollary, Protococcus
and other algal cells living in the open were considered to be escaped
gonidia or, as Wallroth 5 termed them, " unfortunate brood-cells," his view
being that they were the reproductive organs of the lichen plant that had
failed to develop.
It was a step forward in the right direction when lichens were regarded
as transformed algae, among others by Agardh 6
, who believed that he had
followed the change from Nostoc lichenoides to the lichen Collema limosum.
Thenceforward their double resemblance, on the one hand to algae, on the
other to fungi, was acknowledged, and influenced strongly the trend of study
and investigation.
The announcement 7
by Schwendener 8 of the dual hypothesis solved the
problem for most students, though the relation between the two symbionts
is still a subject of controversy. The explanation given by Schwendener,
and still held by some 9
that lichens , were merely fungi parasitic on algae,
was indeed a very inadequate conception of the lichen plant, and it was hotly
contested by various lichenologists. Lauder Lindsay 10 dismissed the theory
as "
merely the most recent instance of German transcendentalism applied
1
Luyken 1809.
8 Wallroth 1825.
9 Fink 1913.
2 Hornschuch 1819.
3 Raab 1819.
6 Agardh 1820. 7 See p. 27.
10
Lindsay 1876.
4 Dillenius 1741, p. 200.
8 Schwendener 1867.