IOWA ACADEMY OP SCIENCES 
6T' 
possible that we frequently bring into existence elementary varieties of 
bacteria and yeast plants partly physiological and partly morphologicalr, 
by cutivation on various media and by transferring from host to artificial 
media. The life cycles are often short among lower plants, and this 
advantage would serve to offset, in part, some other difficulties; and 
the physiological considerations of relation to substratum, ever becoming 
of greater and greater importance in the systematic studies of species, 
may be investigated without great difficulty. 
Since the fusion of sexual nuclei has come to be regarded as a potent 
cause of variation, we may doubt whether rapid evolution may be 
expected in some of the lower algae and fungi. But in the low unicell- 
ular and filamentous forms, division, which corresponds to vegetative 
reproduction higher up, may bring a form of evolution comparing with 
bud variation in higher plants. Yet on the whole, we may expect muta- 
tion, if such a phenomenon exists among lower plants, to follow the 
fusion of sexual nuclei more readily than any form of vegetative fusion 
or vegetative or asexual reproduction. However, recent researches have 
greatly widened the known range of sexuality among lower plants, 
so that we may now approach the problem of evolution through sexual 
fusion among lower plants with more confidence than formerly. 
That our views regarding lichen species and varieties are, and always 
have been, quite crude and often unscientific is apparent enough to one 
w^ho has attempted to do extended taxonomic work within the group. 
Many of the names of species date back to Linnaeus’ time, when the 
views regarding species in general were necessarily based upon a very 
limited amount of observation and were in the main also tainted by the 
quite prevalent belief in independent creation. 
Also with the recent light as to the real nature of the so-called lichen 
plant, it may w^ell be doubted as to whether we really are at liberty to 
conceive of any other species than taxonomic, admitted for the sake of 
expediency in classification. Yet, examining a little closer, it appears to 
the observer and student of lichen forms that in many instances species 
or varieties have arisen from a given form since the association of the 
two symbionts began. Here then, w-hether we admit with Rienke and 
Schneider, that a lichen is after all to be regarded as a morphological 
and physiolcgical unit, we surely seem to have species arising in the 
usual way, either by fluctuations or by mutations. Thus it appears that, 
whatever view one may take as to the nature of the lichen, he must treat 
any discussion of species as though lichens were undoubted autonomies. 
But there seems to be at least one very peculiar view as to the lichen- 
species. And that is the idea entertained by some botanists that liclien 
species cannot properly be based on morphological characters, since the 
lichen is not a morphological unit and has not, even as a symbiotic 
association, acquired any very fixed morphological characters. These 
botanists, instead of continuing to base our taxonomic lichen-species 
upon morphological characters, or in part upon physiological relations 
