een followed further than the
development of a hypothallus, it might be accounted for by the absence
of the essential algal on which the new organism should become
parasitic; 5th. That there is a striking correspondence between the
development of the fruit in lichens and in some of the sporidiiferous
fungi (_Pyrenomycetes_).

These five points have been combated incessantly by lichenologists,
who would really be supposed by ordinary minds to be the most
practically acquainted with the structure and development of these
plants, in opposition to the theorists. It is a fact which should have
some weight, that no lichenologist of repute has as yet accepted the
theory. In 1873 Dr. E. Bornet[L] came to the aid of Schwendener, and
almost exhausted the subject, but failed to convince either the
practised lichenologist or mycologist. The two great points sought to
be established are these, that what we call lichens are compound
organisms, not simple, independent vegetable entities; and that this
compound organism consists of unicellular algae, with a fungus
parasitic upon them. The coloured gonidia which are found in the
substance, or thallus of lichens, are the supposed algae; and the
cellular structure which surrounds, encloses, and imprisons the
gonidia is the parasitic fungus, which is parasitic on something
infinitely smaller than itself, and which it entirely and absolutely
isolates from all external influences.

Dr. Bornet believed himself to have established that every gonidium of
a lichen may be referred to a species of algae, and that the connection
between the hypha and gonidia is of such a nature as to exclude all
possibility of the one organ being produced by the other. This he
thinks is the only way in which it can be accounted for that the
gonidia of diverse lichens should be almost identical.

Dr. Nylander, in referring to this hypothesis of an imprisoned
algal,[M] 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 the spleen constitutes parasites of the
mammiferae. Parasite existence is autonomous, living upon a foreign
body, of which nature prohibits it from being at the same time an
organ. This is an elementary axiom of general physiology. But
observation directly made tea