92 



SCIENCE 



[N. S. Vol. XXIX. No. 733 



of contradiction that all scientific botanists 

 hold that the vegetable kingdom as we know 

 it to-day is the result of a series of evolu- 

 tions from lower to higher types of plants, 

 and that every higher plant owes its present 

 sti'ucture to the favorable modification of 

 sou. 9 ancestral lower plant. To-day when 

 we study the particular structure of any 

 plant we consider it to be the result of the 

 modifications that have taken place in its 

 phylogenetic history. No botanist now 

 considers a species to be a separate or 

 special creation, but rather a more or 

 less distinguishable variation from some 

 other form. 



"With such an agreement among botanists 

 as to the validity of the doctrine of evolu- 

 tion, it needs no argument to sustain the 

 thesis that a natural classification must- 

 be an expression of a theory of evolu- 

 tion. Such taxonomic terms as "higher," 

 "lower," "primitive," "derived," "rela- 

 tionship," "affinity," etc., can have no 

 other significance than that given them by 

 the doctrine of evolution. To-day there are 

 no hidden or occult meanings to be attached 

 to plant structures. We no longer credit 

 the doctrine of signatures, whether in med- 

 ical or systematic botany. We no longer 

 seek to find the characters which in some 

 mysterious way are the special marks of 

 classes, nor those which are necessarily 

 ordinal marks, or the characteristic marks 

 of families, and so on to genera and species. 

 And yet it is not so very long since a great 

 biologist seriously set about trying to do 

 this very thing. You will remember that 

 Agassiz made this attempt^ about fifty years 

 ago, and that he actually formulated his 

 plan in definite terms. I may as well quote 

 the paragraphs in which he states his 

 method of characterizing different groups. 

 They are as follows: 



' " An Essay on Classification," by Louis Agas- 

 siz, London. The preface dated December, 1858, 

 p 261. 



Branches or types are characterized by the plan 

 of their structures; 



Classes, by the manner in which that plan is ex- 

 ecuted, as far as ways and means are concerned; 



Orders, by the degrees of complication of that 

 structure ; 



Families, by their form, as far as determined by 

 structure ; 



Genera, by the details of the execution in special 

 parts; and 



Species, by the relations of individuals to one 

 another and to the world in which they live, as 

 well as by the proportions of their parts, their 

 ornamentation, etc. 



With regard to these he says a little later' 

 that "the branches, the classes, the orders, 

 the families, the genera, the species, are 

 groups established in nature respectively 

 upon different categories," and declares 

 that he feels "prepared to trace the natural 

 limits of these groups by the characteristic 

 features upon which they are founded," 

 that is, upon those which have just been 

 enumerated in my quotation. 



In the common systematic characters as 

 drawn up by many botanists in the recent 

 past there has been something of the old- 

 time notion that we are dealing with fixed 

 groups whose limits are indicated to us by 

 certain rather definite structural characters 

 which nature has accommodatingly at- 

 tached to all plants in these groups. The 

 thought seems to have been that plants are 

 "tagged" or "branded" with the peculiar 

 marks of the group, these marks having 

 otherwise no particular significance. One 

 is reminded of the similar use which stock- 

 men on the plains make of arbitrary names, 

 monograms or hieroglyphics for indicating 

 what animals belong to this or that par- 

 ticular ranch. And it appears that this 

 view of the meaning of taxonomy and the 

 significance of characters has not wholly 

 died out. The most reasonable explanation 

 of the inordinate species making practised 

 by some botanists is that they are still under 



• " An Essay on Classification," p. 263. 



