12 FUNGI. 
substance, or thallus of lichens, are the supposed alge; and the 
cellular structure which surrounds, encloses, and imprisons tne 
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 algw, and 
that the connection between the hypha and gonidia is of such a 
nature as to exclude all possibility of the one organ being pro- 
duced 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,* 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 mammifera. 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 physiolozy. But observation 
directly made teaches that the green matter originally arises 
within the primary chlorophyll- or phycochrom-bearing cellule, 
and consequently is not intruded from any external quarter, nor 
arises in any way from any parasitism of any kind. The cellule 
at first is observed to be empty, and then, by the aid of secretion, 
green matter is gradually produced in the cavity and assumes a 
definite form. It can, therefure, be very easily and evidently 
demonstrated that the origin of green matter in lichens is en- 
tirely the same as in other plants.” On another occasion, and in 
another place, the same eminent lichenologist remarks,t as to 
the supposed algoid nature of gonidia—“ that such an unnatural 
existence as they would thus pass, enclosed in a prison and 
* Nylander, ‘¢On the Algo-Lichen Hypothesis,” &c , in ‘‘Grevillea,” vol. ii. 
(1874), No. 22, p. 146. 
+ In Regensburg ‘‘ Flora,” 1870, p. 92. 
