TAXONOMIC PRINCIPLES 35 



by several generations of taxonomists, each generation adding obser- 

 vations and concepts to the preceding. Descriptive data were compiled 

 for the lower taxa first and their significance and limitations deter- 

 mined before meaningful interpretations and circumscription of the 

 higher categories could be made. Many errors were forthcoming in the 

 extrapolations and interpretations incidental to its construction, but, 

 over-all, the resulting taxonomic structure rests on a solid foundation 

 of observational fact as opposed to mere conjecture. 



Phylogenetic knowledge of both the major and minor catego- 

 ries of classification is certain to advance as our knowledge of 

 biochemistry advances. To be sure, the ultimate proofs of the system 

 must depend on the evidence from all fields, mainly paleobotany, but 

 we can no longer tacitly assume that "... a natural classification must 

 in the main be based on external characters, simply on account of the 

 much larger number of these and their much more restricted inci- 

 dence" (Sprague, 1940). There is a wealth of biochemical data awaiting 

 exploration, and, while the gross examination of leaves and floral parts 

 might be the most practical method for the classification of most 

 plants today, the chemical approach is certain to add significantly to 

 any ultimate phylogenetic system. Even at the level of identification 

 there is a significant advantage to the biochemical approach, for if an 

 exomorphic taxonomist were asked to identify a plant from a leaf or 

 petal fragment he might despair, but given chemical data he might be 

 able to identify the fragment to species. This can be done with 

 certainty in the case of the species of Baptisia so far examined 

 chemically. 



