INTRODUCTION. 19 



grouping of yesterday unscientific and archaic to-day. Popu- 

 lar manuals, wherever they may be published, however pains- 

 takingly and skilfully they may be compiled, are always dis- 

 tinctly in the rear of actual botanical advancement in that 

 group which they propose to elucidate. The well-known and 

 reasonable demand for stability in nomenclature is sometimes 

 accompanied by an unreasonable demand for permanence 

 of classification, but if such a demand could be granted it 

 would indicate absolute stagnation in botanical or zoological 

 science, such as can not, under present intellectual conditions 

 of the race, readily be conceived. While, therefore, the constant 

 shifting from one classification to another is exasperating to 

 the conservative student, it is nevertheless a necessary result 

 of advancing information, and to refuse to consider the new 

 systems which may be put forth in scientific fashion is as 

 unreasonable as it was in those days when the railway carriages 

 were first brought into use for one to insist upon travelling by 

 the old stage-lines of an earlier mechanical era. 



The vegetable kingdom becomes more and more difficult to 

 arrange in well ordered groups as one's knowledge of its com- 

 plexities and relationships increases. The old notion, for ex- 

 ample, that it is possible to divide plants into those with flowers 

 and those without, by an arbitrary demarcation-line, has grad- 

 ually disappeared as more and more information has been col- 

 lecting regarding the life-histories and homologies of such 

 transition types as Selaginella, Isoetes, Cycas, Gasuarina or 

 Marsilia. The two divisions seen so clearly by Linnaeus have 

 come to merge into each other and must be defined to-day in far 

 different terms than in 1735. And again the old divisions of the 

 Dicotyledones — Polypetalae, Apetalae and Gamopetalae — have 

 been found to be untenable, for they serve to separate into dif- 

 ferent groups, genera which from a preponderance of charac- 

 ters are generally believed to be closely related. Under the 

 stress of renewed examinations the Polypetalae and Apetalae 

 have been combined and in this work the combination-name 

 applied is Archichlamydeae. These serve as examples of 

 changes in nomenclature resulting from changes in view-points 

 under increased knowledge. 



It will be appropriate to give, in this introduction, a word or 

 two to the later methods of plant- classification. Mention may 

 be made, very briefly, of the basis of such classification. In 

 the first place, a survey of the vegetable kingdom reveals that 

 all the forms known to us may be thrown into two groups 



