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, thatit 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, Casuarina 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 
