4 
Ohio I Biological Survey 
therefore forming no part of it. Some of the arguments for this position 
may lie reviewed liriefiy. The algal host is in a disadvantageous position 
with respect to light and food materials. The cells of the host become 
large and may divide rajiidly because of undue stimulation, showing a 
hypertrophied and pathologic condition, resulting in marked vegetative 
activity, which balances the rai)id killing of the algal-host individuals. 
The bright-green, normally-shaped, algal individuals seen in lichens are 
usually those that are not yet parasitized, or those that have been recently 
parasitized. The relationship between the lichen and the alga is peculiar 
on account of the sim])le structure of the latter; but the lichen seems to 
be a parasite or a saprophyte, or perhaps partly a parasite and partly a 
saprophyte, on the alga. The haustoria of lichens are similar to those 
of other fungi and in all probability function in like fashion. For an 
extended discussion, see the paper hy Fink (31). 
One cannot deal with colonies in studies of ontogeny, phylogeny, 
mori)hology, or taxonomy, nor does the use of Collcma piilposurn, Plivscia 
stcllaris, or other binomial by one group of botanists to designate a plant 
and by another group to designate a compound colony conduce to clear¬ 
ness. In order that one may be clear in his thinking regarding lichens, 
he must abandon the historical idea that the chlorophyllous cells found 
in these plants, or in which the lichens live in a few instances, are part 
of the lichen, or he must hold consistently to the view that the lichen is 
not a plant, but a compound colony. Critical examination of statements 
about lichens by a large number of botanists shows that it is not possible 
to regard the lichen in one of these ways for one purpose and in another 
manner for another purpose, or even to consider the compound colonies 
for one purpose and the fungi of the colonies for another purpose, with¬ 
out committing some of the inconsistencies so commonly found in state¬ 
ments about lichens (see discussion in Fink 31). The conclusion that 
the lichen is a fungus is the only one that can be followed equally well 
by the physiologist, the ecologist, the morphologist, the cytologist, and the 
systematist. In a previous paper (Fink 31), the typical lichen has been 
defined as a fungus which lives in parasitic relationship with an alga 
during all or part of its life, and also sustains a relationship with an 
external substratum, organic or inorganic. The lichens will be dealt 
with according to this definition in the treatment of the ascomycetes 
throughout this series of papers. 
Idchens possess few distinct characters other than physiological, and 
these have no weight in the classification of these plants. The dual 
hypothesis can scarcely be considered seriously in view of recent studies 
