APPLICATIONS 13 
lationships will depend largely upon the gap existing between the families 
concerned. While interpretation will always play a part in taxonomy, the 
general use of experiment will leave much less opportunity for the personal 
equation than is at present the case. Taxonomy, like descriptive botany, is 
based upon the species, but, while there may exist a passable kind of de- 
scriptive botany, there can be no real taxonomy as long as the sole criterion 
of a species is the difference which any observer thinks he sees between one 
plant and another. The so-called. species of to-day range in value from 
mere variations to true species which are groups of great constancy and 
definiteness. The reasons for this are obvious when one recalls that “spe- 
cies” are still the product of the herbarium, not of the field, and that the 
more intensive the study, the greater the output in “species.” It would 
seem that careful field study of a form for several seasons would be the 
first requisite for the making of a species, but it is a precaution which is 
entirely ignored in the vast majority of cases. The thought of subjecting 
forms presumed to be species to conclusive test by experiment has appar- 
ently not even occurred to descriptive botanists as yet. Notwithstanding, 
there can be no serious doubt that the existing practice of re-splitting hairs 
must come to an end sooner or later. The remedy will come from without 
through the application of experimental methods in the hands of the ecol- 
ogist, and the cataloguing of slight and unrelated differences will yield to 
an ordered taxonomy. 
Experimental evolution will solve a taxonomic problem as yet untouched, 
namely, the effect of recent environment upon the production of species. It 
is well understood that some species grow in nature in various habitats 
without suffering material change, while others are modified to constitute a 
new form in each habitat. It is at once clear that these forms (or ecads) 
are of more recent descent than the species, i. e., of lower rank. It must 
also be recognized that a constant group and a highly plastic one are essen- 
tially different. If constancy is made a necessary quality of a species, one 
is a species, the other is not. If both are species, then two different kinds 
must be distinguished. Among the species of our manuals are found many 
ecads, alongside of constant and inconstant species. These can be distin- 
guished only by field experiment, and their proper coordination is possible 
enly after this has been done. Indeed, the whole question of the ability or 
the inability of environmental variation to produce constant species is one 
that must be referred to repeated and long-continued experiment in the field. 
A minor service of considerable value can be rendered taxonomy by 
working over the diagnosis from the ecological standpoint. Many ecological 
facts are of real diagnostic value, while others are at least of much interest, 
and serve to direct attention to the plant as a living thing. The loose use of 
