106 
Mycologia 
uals. Ecological and physiological studies of the lichen and the 
alga with which it lives are just as interesting and more compre- 
hensible when these plants are considered in their proper rela- 
tion as independent but intimately associated organisms. Fur- 
thermore, this method in plant physiology and ecology would aid 
in bringing botanists into general accord as to method of treating 
these plants, and would thereby help do away with the incon- 
sistency and confusion which make it so difficult for botanists to 
express themselves in a coherent manner regarding lichens. The 
physiologists and the ecologists have been less inclined than tax- 
onomists to depart from the traditions concerning lichens ; but 
they may well ponder carefully the latest views of leading 
Hellenists (55), who are as much disposed to think that lichens 
are fungi as are other morphologists and taxonomists. The one 
argument in recent years for not considering the lichen a fungus 
pure and simple has been the supposed mutualistic relation of the 
lichen to the alga, and this has been made to appear untenable 
by the recent researches of Danilov, Elenkin, Peirce and others 
cited above. In view of these investigations, it would seem that 
plant physiologists and ecologists, especially, should abandon the 
dual hypothesis, which is not tenable in any form or under any 
condition of mutualism and is wholly unreasonable if it is ad- 
mitted that the relation of the lichen to the alga is antagonistic. 
The researches bearing on this problem are considered at length 
toward the close of this paper. 
Difficulties to Be ]\Iet in Tre.\ting Lichens as Fungi 
Plainly, the only consistent view is that the lichen is a fungus. 
But having reached this position, there is difficulty enough for 
mycologists, especially those that study Ascomycetes, to which the 
lichens very largely belong. Botanists seem, as a rule, to think 
that the relationships of lichens to other Ascomycetes should be 
ascertained by Hellenists, while students of non-algicolous Asco- 
mycetes, trained as badly in this matter as are the Hellenists, con- 
tinue to avoid the study of algicolous Ascomycetes. This position 
seems wholly unreasonable. If we are ever to know the relation- 
ships of algicolous to non-algicolous Ascomycetes, lines of cleav- 
age in study must cease to be determined by the food habits of 
