THE DUAL LICHEN HYPOTHESIS. 
119 
chemical preparation ; and in favourable cases, I have even seen 
them with the non-immersion lower powers of Hartnack.” He 
proceeds to say that these micro-gonidia are paler than the ordinary 
gonidia, and disposed in moniliform series in the axes of the 
hvphse, having a diameter of *001 mm. In certain tropical species, 
which had been exposed to a more vivid light than those in more 
northern latitudes, these micro-gonidia attained a brighter green; 
for example, in Parmelia prolixa , var. erythrocardia , MiilL, sent 
by Dr. Schweinfurth from Lake Nyanza, in Africa. In this Lichen 
they were so green that little difference of colour existed between 
them and the gonidia.* 
If the “ parasite ” can produce within itself all which it requires 
for its existence, then Nature has made a mistake in making it 
dependent on another being for its existence. 
Here, then, we have clear demonstration that the gonidia are 
developed within the substance of the Lichen itself in a determi- 
nate and uniform manner ; that, instead of being altogether foreign 
from the Lichen, they are generated within it, and hence (according 
to the hypothesis) the parasite produces from its own substance 
the host upon which it is parasitic. 
The admirable Memoir of Tulasne should be consulted in con- 
junction with Dr. Minks’s contributions to the “Flora,” and it 
will be seen that the latter confirms and amplifies the former, 
adding thereto new facts, and thus, doubtless, establishes the true 
relationship of gonidia to the residue of the Lichen. 
I am compelled to be suggestive, rather than exhaustive, in 
dealing with such an expansive subject, which I scarcely regret 
here, because it bears less intimately than others upon that phase 
of the subject in which I am naturally most interested. 
Is Parasitism proven ? — A parasite is usually defined as an animal 
or plant which lives upon or attaches itself to another, and derives 
therefrom sustenance and support. The mistletoe, which attaches 
itself to poplar and other trees, is a parasite. The mould which 
attacks and destroys potatoes, is a parasite, entozoa are parasites, 
and so also are the pediculi, and other insects which infest the 
higher animals. In ordinary conversation there is seldom likely 
to be any misconception of what is a parasite. In all known 
instances of parasitism, it is, I presume, admitted that the parasite 
thrives and flourishes at the expense of its host. In every known 
instance of parasitic fungi the fungus lives at the expense of its host, 
which it injures and ultimately destroys. Schwendener himself says, 
“ the vine and potato fungus, as well as all other fungi which vegetate 
in living organisms, destroy their host plant, or host animal, in the 
unequal struggle.” This universality of destructive parasitism in 
fungi knows no exception, and is, therefore, equivalent to a natural 
law. Any hypothesis which depends upon fungal parasitism, must 
of necessity recognize this fact, and conform to it. The fact can- 
not be reversed to save the hypothesis. 
* Consult Minks on Micro-gonidia, in the “ Regensburg Flora,” for 1878. 
