176 BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 3, NO. 4-. 
of the case, appear in the higher taxonomic groups as genus, 
family, order, etc., and an examination of their characters shows 
that this is rather more apparent than real. A genus, family, or 
order is only a group of characters, whose definite variants form 
the next lower class. As a genus is only a group of characters 
it can have no definite life, no individuality, and there can be no 
determinate influence working upon it ; it can only exist in the 
fact that a group of variants, species, unite in having common 
characters. The species is the nearest possible approach to tax- 
onomic unity, as it is by conception the group having the largest 
number of common characters ; to carry the division one step 
farther into the individual would result in a wholly natural 
classification i. e. chaos in our artificial systems. As the species 
is only a group of individuals profiting by adjustment to a hospi- 
table sum of contacts it follows that the genus exists only in the 
fact that certain elements in this sum of contacts are common to 
the group of species. So long as the environment retains a fun- 
damental group of contacts, so long will the species having com- 
mon characters i. e. the genus, persist. The mutation of a genus 
is the slow accommodation of a group of species to a fundamental 
change in the environment while around this play a large num- 
ber of specific changes due to the less important but more obvious 
changes in the environment. 
Mutations are not in defiance of the environment but a close 
response to its fundamental most slowly changing elements. 
Williams in his distinction between mutation and variation does 
not use this point of view. He says. Bull, U. S. G. S. p. 210, varia- 
tions are "differences expressed by specimens of the same species 
— differences arising coincidentally with extension of geogra- 
phical distribution and changes in condition of the environment." 
Mutations are "changes of form that are coincident with passage 
of time, and hence to generational succession under conditions of 
life so nearly the same that extinction of the race does not result." 
This is the idea of Scott's Mutations and Osborn's Definite Evo- 
lution ; the idea here proposed is that mutation is as much a re- 
sponse to the changing environment as variation but that it is 
the visible concurrence of different species in a common line of 
change determined by the fundamental features of the environ- 
ment and their change. 
It is interesting just at this point to examine somewhat the 
work of DeVries and Burbank in the light of a possible expla- 
nation, on this line. DeVries work was, as all know, done on a 
species of Primrose, some times referred to as the Asses Weed, 
