248 THE AMERICAN NATURALIST. [Vor. XXXIV. 
the fungus from spore to spore, and whether or not we believe 
with him that the fungus components of lichens no longer 
exist by themselves in nature, we certainly must call them 
fungi. 
What isa fungus? However a systematist might answer this 
question, a physiologist would say that a fungus is a low de- 
pendent plant, demanding at least non-nitrogenous food in a 
state of comparatively high elaboration (sugar, fat, oil, or simi- 
lar carbon compounds), since it is unable to manufacture such 
food for itself. It follows, therefore, that a fungus must be 
either parasitic or saprophytic, or, to follow the newer terminol- 
ogy,! metatrophic or paratrophic. When a fungus enters into 
association with an alga to form a lichen, the fungus allies 
itself with an independent plant, one able to manufacture all 
of its own food. The lichen is then composed of a dependent 
plant which must receive elaborated food, and of an independ- 
ent plant which needs only food materials and light in order to 
take care of itself. What then is the nature of the association 
between these two? Reinke? and his sympathizers believe (a) 
that the association is consortism; (4) that the two members 
of the consortium are dependent upon and beneficial to each 
other; and (c) that the consortium is autonomous. On the 
other hand, many botanists, probably in the minority at the 
present moment, see in this association not a mutually advan- 
tageous association, but the parasitism of one plant upon 
another. Reinke, de Bary,* and many others assert that the 
association of fungus with alga in lichens cannot be simple par- 
asitism because, if this were the case, the fungus would con- 
sume the alga, and that would be the end of the association. 
Such a conclusion is not required by the evidence. It must 
first be shown that the influence of the fungus is so violent and 
so exhausting that the alga is not able, by producing slightly 
more food, by refraining from less economical ways of repro- 
1 Fischer, A. Vorlesungen über ras pp- 47, 48. Jena, r897. 
2 Reinke, J. Abhandlungen iiber Flechten. II. Die Stellung der Flechten im 
sherman prim i f. Wiss. Bot., Bd. xxvi, pp. 524-542, 1894. 
Reinke, J cit., Bd. xxvi, p. 530, etc. 
* de Bary, A. Die Erscheinung der Symbiose. Strassburg, 1879. 
