2I20 A TEXTBOOK OF THEORETICAL BOTANY 



has, naturally, been confusing and of late years the need for a philosophical 

 examination of the principles of taxonomy has been felt more and more 

 widely. The outcome of enquiry and discussion has been very helpful in 

 clearing up ideas, though some fundamental differences of opinion have 

 not yet been reconciled, particularly between botanists and zoologists, and 

 it cannot be claimed that anything like finality has been reached. Doubts 

 still exist whether there is, in fact, an ideally perfect classification which 

 may be accepted as an aim of taxonomy and, again, whether phylogeny can 

 ever be fully expressed in classification. If evolution could be represented, 

 as used to be thought, by a " phylogenetic tree " there might be hope of 

 arranging organisms in a corresponding pattern, but attempts to formulate 

 such patterns have not been encouraging and botanical opinion is more 

 inclined to agree with the expressed view that " the phylogenetic order is 

 not so much a tree as a bundle of sticks." 



Since one of the primary objects of classification is to produce order, 

 practical convenience cannot be ruled out, and no classification, however 

 ideal scientifically, can be based upon data which are not available. This 

 undeniable necessity of practice, however, conflicts with the fact that 

 organisms may differ, permanently and heritably, in features w^hich can 

 only be ascertained by intensive investigation of the living plants and are 

 therefore only available in a few cases. This is the dilemma which lies at 

 the root of much of the uncertainty and lack of uniformity which pervade 

 the history of classification and are so puzzling to the student and so 

 hampering to the investigator. 



The problem is basically a philosophical one and the consideration of it, 

 from this point of view, has only begun, but at least one important conclu- 

 sion, which bears directly upon our difficulty, may be cited. This is the 

 conclusion that the conflict is not between subjective concepts and objective 

 things or between mind and matter, but that all the units of classification of 

 whatever grade, the taxa, to use a general term, i.e., varieties, species, 

 genera, etc., are alike in being mental constructions from sense data. The 

 latter are " real " in a material sense, but the units into which we group these 

 data, whatever their character, are rational constructions of our minds and 

 their nature ultimately depends, therefore, on the ego of the observer, who 

 may prefer purely logical principles, or who may attempt, alternatively, to 

 form his constructions on what he believes to be a " natural " model. 



The former was the preference of pre-evolutionary systematists who 

 formed the " artificial " systems which were characteristic of the seventeenth 

 and eighteenth centuries. In these systems logic was the ruling principle 

 and convenient order was the end pursued. They were, in varying degrees, 

 satisfactory for their proposed objects and the most completely logical of 

 them, the Sexual System of Linnaeus, enjoyed wide and prolonged accep- 

 tance. Nevertheless, the natural model refused to be ignored. From the 

 beginnings of biological science man had intuitively recognized certain 

 groupings of plants as realities, e.g., Umbelliferae and Compositae, and a 

 logical arrangement which did violence to this feeling was deemed unsuc- 



