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 

 only 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 



