18 BIOCHEMICAL SYSTEMATICS 



(1959), in setting forth his views on the phylogeny of angiosperms, 

 adopts the principle that "the spiral arrangement of leaves on the stem 

 and of the floral leaves precedes that of the opposite and whorled type." 

 However, Cronquist (1955), in considering the phylogeny of the 

 family Compositae, considered opposite leaves to be the primitive 

 condition for the family, but this need not mean that he considers 

 this to be a primitive character for the angiosperms generally. 

 Similarly, Hutchinson's view that the herbaceous habit is primitive 

 in the Ranunculaceae does not conflict with his supposition that 

 woodiness is a primitive condition for the angiosperms generally. 



Practically all of these principles concern morphological 

 features, but it is not unlikely that as studies of "molecular evolution" 

 (Anfinsen, 1959) develop there will be as many, if not more, principles 

 formulated from purely chemical data. At least one worker (McNair, 

 1945) has ventured, though prematurely, into this field of conjecture, 

 and others are sure to follow. 



Many of the more recently proposed classificatory systems 

 are accompanied by schematic diagrams showing the relative taxo- 

 nomic positions of the taxa treated. Lam (1936) has written an excel- 

 lent summary of such presentations, some of which are rather bizarre. 

 Little advance in this type of symbolization has occurred since Lam's 

 review of the subject. Most workers have presented their diagrams in 

 a two-dimensional framework, mainly because fossil data are lacking 

 to substantiate speculations in time. However, some workers, on the 

 basis of several other kinds of evidence, have sought to reconstruct 

 the chronological phyletic history of a given group and thus have 

 added a third dimension, time, to their scheme. Diagrams of the sort 

 mentioned have been constructed for taxonomic groups at all levels 

 from the species to the kingdom (Fig. 2-2 to Fig. 2-7). Most two- 

 dimensional schemes are presented merely to show relative similarities 

 and differences between taxa, although attempts are sometimes made 

 to include the "lines of evolution" for the taxa concerned, usually with- 

 out time connotations. 



Two-dimensional phylogenetic diagrams 



The two-dimensional presentation is popular because it is 

 simple to construct and need not reflect phylogeny, though it would 

 usually imply that the presentation was the best approximation from 

 the data at hand. One popular form of the two-dimensional scheme 

 is that shown for the genus Dicentra (Fig. 2-4). While phylogenetic 

 lines are shown in this scheme and the relative positions of the 



