TAXONOMIC PRINCIPLES ]7 



derivatives (when present) of any taxon. The present state of man's 

 knowledge of nature is too scant to enable one to construct a phylo- 

 genetic classification, and the so-called phylogenetic systems represent 

 approaches toward an objective and in reality are mixed and are 

 formed by the combination of natural and phylogenetic evidence. 



In the discussion below we vdll confine our attention primarily 

 to those systems of a phylogenetic nature. Artificial systems are no 

 longer used by the professional taxonomist, and since as indicated 

 earlier truly natural and truly phylogenetic systems are theoretically 

 synonymous, there is little need to prolong a distinction between 

 the two except in a historical-philosophical sense such as Lawrence 

 has done. 



After Darwin's work there began to appear numerous and 

 varying systems of classification, nearly all of which were based on 

 phylogenetic considerations. Turrill (1942) has perhaps justly criti- 

 cized much of this speculation as has Lam (1959). The latter author, 

 in particular, emphasized the necessity of fossil evidence before any 

 substantial phylogenetic classification might be achieved, and he dis- 

 tinguishes between systems erected on the basis of "static taxonomy" 

 (proposed without paleobotanical data) and systems based on 

 "dynamic taxonomy" (utilizing fossil data). 



Since, in the case of most flowering plants, nothing resembling 

 a progressive fossil sequence exists equivalent to the classic zoological 

 examples (for example, horse, ammonites, and so on), nearly all sys- 

 tems of classification for the group are based frequently on arbi- 

 trary principles as to what constitutes primitiveness or, in turn, 

 advancement. 



Over fifty such principles have been advanced, some of a 

 contradictory nature depending on the point of view of the systema- 

 tist (Just, 1948; Constance, 1955). For example, Engler and Diels 

 (1936) considered that the majority of plants with simple unisexual 

 flowers were primitive, while Bessey, Hutchinson and others have 

 considered these same floral types indicative of advancement, the 

 condition having developed by reduction processes from complete, bi- 

 sexual flowers. The bases for some of the principles are well docu- 

 mented by extensive, detailed correlative studies on both living and 

 extinct groups (for example, the derivation of vessels from tracheids; 

 Bailey, 1944), while other principles are based more or less on a priori 

 judgment (for example, the assumption that free petals are more 

 primitive than connate petals, and so on). It should also be empha- 

 sized that any evaluation of the various principles must be considered 

 with respect to the group under examination. Thus Hutchinson 



