FINK—THE LICHENS OF MINNESOTA. 7 
Setting out from this conception of the relationship of the two sym- 
bionts, botanists began to classify lichens as fungi. ; 
In other instances of symbiosis than that found in lichens one or 
each of the symbionts is able to live quite independently of the other. 
In certain lichens the alga has been isolated from the association and 
has grown and produced reproductive bodies. Likewise the fungi 
forming some lichens have been isolated and have produced, in 
nutritive media, forms resembling the ordinary thalli of the lichen 
species. However, it may well be doubted whether either the fungal 
or the algal symbiont ever becomes free in nature and lives during its 
whole life period outside the symbiotic association. Thus, we seem 
to have in lichens the highest expression, so far as it is known, of 
mutualism. The alga does not reproduce in the association, except 
by fission, but it is protected in such a manner that it can grow where 
it could not otherwise, and its continued existence, or the succession 
of individuals rather, is assured. And though the fungal symbiont 
produces various reproductive bodies, it may well be doubted whether 
any reproduction other than vegetative often takes place in lichens 
ina state of nature. Again, it is evident from observation, that 
many new species of lichens have been evolved from closely related 
species. Thus the lichen, after all, in many ways appears much like a 
morphological unit, and J. Reinke has arrived at the conclusion that 
it must be so regarded, and has succeeded in unsettling to some 
extent the idea that lichens should be regarded as fungi. 
Some botanists still hold that the relationship of the fungus and 
the alga is antagonistic. Whatever may be the outcome of further 
study of this question, the conception brought out in the above 
historical review, which is still held by some botanists, that the 
fungus and the alga together compose an organism or an association 
which constitutes the lichen must be abandoned before there can be 
any clear thinking regarding lichens. The lichen is the fungus of the 
association. This is true even in the few instances in which the alga 
determines the form of the thallus. 
Certain botanists regard it as a corollary of this conclusion that, 
from a strictly systematic point of view, lichens should be distributed 
as fungi and some workers have already taken this position;¢ but 
there are still some lichenists and other botanists who would be 
pleased with no other statement than that lichens compose a distinct 
group of plants. In view of the lack of agreement among authorities 
and for strong practical reasons it is not held advisable to undertake 
the distribution of lichens as fungi in the present paper. 
a@See Bessey’s “A Synopsis of Plant Phyla.’ University of Nebraska Studies 
7: 1-99. 1907, and Clements’s, ‘*The Genera of Fungi,” 1909, briefly reviewed in 
ScIENCE; n. ser, 30:567, 568. Oct, 22, 1909. 
