MERRILL: FXONOMIC ASPECTS OF TAXONOMY 55 



ering plants, than the dicotyledons and the monocotyledons. Or we may select 

 to follow the Endlicher system as developed by Engler and Prantl, treating the 

 gymnosperms first, then the monocotyledons and finally the dicotyledons ; or 

 we may decide with Wettstein and others, that the dicotyledons should be 

 placed before the monocotyledons if the system is to be a " natural one, in 

 accordance with various lines of evidence as to the comparative times of 

 development of these last two groups. 



It is inevitable that when a proposed system becomes very widely used, 

 like that of Bentham and Hooker, or that of Engler and Prantl, it will become 

 more or less fixed, partly from the weight of authority, partly because of con- 

 venience and for comparative purposes. We may all realize that the Engler 

 and Prantl system of arranging families, in some respects is far from a natural 

 one, and that radical changes are indicated, particularly in reference to the posi- 

 tion, in sequence, of such families as the Magnoliaceae, Ranunculaceae, Ber- 

 beridaceae, etc., which seem clearly to be much more primitive than the 

 Amentales, for example. System after system may be proposed, but relatively 

 few of these will, from the very nature of things, become widely accepted as 

 to the sequence of arrangement of major groups, partly from inertia on the part 

 of working botanists, partly because it is always desirable to be able to make 

 direct comparisons with the work of others, and partly because one is never 

 sure as to just when some morphologist may discover evidence that upsets 

 all previously proposed systems and sets up another "improved" one. It all 

 comes down to the simple fact that within the plant kingdom, when one is deal- 

 ing with such groups as natural families, it is impossible to make any lineal 

 arrangement that will show all relationships and inter-relationships, for devel- 

 opment and differentiation has not followed a straight line from a lower to a 

 higher group, but in many cases it has been divergent, and, we may suspect, 

 reversions have played their part. To indicate natural relationships we must 

 construct variously branched "trees" to show origins and relationships as well 

 as historical sequences ; but in a book we must hew pretty closely to the straight 

 line, whether we are dealing with a series of families in a system of classi- 

 fication, or whether we are dealing in terms of a simple manual for field use, 

 for one page follows another from beginning to end. 



Again, we must always keep in mind that the objects with which we are 

 dealing are variable ; that our accumulated knowledge constantly increases ; 

 that a system that we might set up today, on the basis of the available data, may 

 be outmoded a few years hence when more comprehensive collections, and 

 w4ien a more intensive study of obscure details, perhaps supplemented by 

 anatomic, cytogenetic, genetic, historic, and geographic data, become avail- 

 able. This comment applies more to the problem of species and their inter- 

 relationships than it does to larger categories such as genera and families. All 



