LICHENS. 109 
algal host, but on the contrary excites it to more 
active growth and more enlarged production of 
tissue, then it is clear that it cannot be a fungus, 
but what we have believed it to be, the vegetative 
tissue of a veritable lichen. Mr. Berkeley remarks 
that he had seen the gonidia of a Parmelia, a species 
of foliaceous lichen, originating from hyphe within 
the cells of some drift wood from the Arctic 
regions without the presence of any alga. And 
were any other argument needed to refute the 
hypothesis it might be found in the symmetrical 
and simultaneous growth of lichens, which is 
utterly contrary to what would take place were 
one portion parasitic upon the other, or were 
the lichens compound organisms made up by 
the union of fungi and alge. Whatever may 
be said regarding the parasitism of the gela- 
tinous Collemas,—which might with justice be 
excluded from the lichens altogether,—I do not 
know any alga which could be transformed by 
the influence of any fungus into the highly 
organized texture of the shrubby and foliaceous 
lichens such as Usnea, Cladonia, Cetraria, and the 
higher Parmelias. 
Nature has bestowed upon the lichens a 
peculiar mode of reproduction which appears 
quite different from that of the higher orders of 
the vegetable kingdom ; and yet they are propa- 
