8 VARIATION IN ASTER 
Nor is the species-rank a measure of exact amount of difference. 
The species is a unit which is recognizable and is permanent within 
certain limits of time and environment. Given that permanent 
difference, and we have specific rank; whether the difference 
from its next surviving kindred measure five per cent. of differ- 
ence or thirty. It is unreasonable to expect all the species of a 
genus to be each equally unlike each other; evolution progresses 
faster in one part of a race than in another. It is impracticable 
and wholly undesirable to attempt to give the word species the 
connotation of a certain and exact degree of difference. For instance 
to use the term variety for the forms in which an observer sees two 
per cent. of difference from each other, sz2speczes for those which 
show five per cent., species for those showing ten per cent., super- 
species for those showing twenty, etc., etc., would burden nomen- 
clature, and would restrict and paralyze rather than enlighten. 
We need a short expressive binomial for each species, not a long 
trinomial or a phrase-name which shall locate its rank. Let 
its rank, that is, the amount of its difference, z. ¢., the degree 
of its relationship, be indicated by separate statement in its 
description. 
Some of the species described in these pages are, as I believe, 
young and not as perfectly differentiated as they may yet become. 
Such closely related species may be ignored by some because, 
if species at all, * merely incipient species." Instead, they seem 
to me of utmost interest and most desirable to describe and 
name; to name rather than to indicate merely by number ; for it 
is far easier for the memory to associate given characters with a 
significant name than to attempt to cluster them around an abstract 
and soulless number. In some respects such youthful species 
possess a greater interest than those of old established habit which 
have settled into a state of stable equilibrium. To capture a species 
in the making is indeed one of the prime rewards of research. If 
we are right in judging many of these new species of Aster to be 
of such character (as A. umbelliformis, A. fragans, A. camptilis, 
etc.) we shall find more than ordinary importance attaching to 
them. Therefore we shall not grumble though we find their 
limits uncertain, their characters sometimes baffling and failing in — 
precision, their reversions innumerable, and the direction of their . 
A aces manele Sota and 
NEL REN ge ag Ba T TIERE 
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