108 FIRST FORMS OF VEGETATION. 
which is accustomed to live upon the work of 
others; its slaves are green alge which it has 
sought out, or indeed caught hold of, and com- 
pelled into its service. It surrounds them, as a 
spider its prey, with a fibrous net of narrow meshes 
which is gradually converted into an impenetrable 
covering ; but whilst the spider sucks its prey and 
leaves it lying dead, the fungus incites the algz 
formed in its net to more rapid activity, nay, to 
more vigorous increase.” Other lichenists, such as 
M. Bornet, have adopted this view as the only one 
capable of explaining satisfactorily all that has 
hitherto been observed regarding the nature of 
the thallus of lichens and their fructification. 
But plausible as the hypothesis looks, it seems 
to me to be destitute of foundation. That the 
gonidia of lichens are analogous to or even 
identical with those of algze, and that lichens and 
fungi have between them no absolute. line of 
demarcation, is admitted on all hands; but that 
the relation of the hypha to the gonidia is that 
of the spawn or mycellium of a species of mould- 
fungus to the alga, and such as necessarily to imply 
the idea of the one being parasitic upon the other, 
may be more than doubted. It is well known 
that parasitic fungi destroy the living organisms 
upon which they fasten; and if this assumed 
parasitic fungus does not destroy its assumed 
