CHAPTER XXXI 



THE CLASSIFICATION OF PLANTS 



The subject of Plant Classification includes three aspects which are distinct 

 in theor}% although they necessarily overlap in practice. Firstly, there is 

 taxonomy, the " law of order", which is the study of the principles on 

 which classification is, or should be, based. Secondly, systematics, which 

 implies the determination of the groupings to be used and their relative 

 positions in a system. Thirdly, nomenclature, or the study of the correct 

 naming of the groups employed, according to the generally accepted rules. 



All three disciplines have the convergent aim of fixing the names of 

 organisms and of their groups. The identity and the relationships of an 

 organism are embodied in its name and without agreement on this matter 

 every form of botanical enquiry is rendered nugatory. As Linnaeus said: 

 Pereiint noniina perit et cognitio renim. Agreement in nomenclature is still 

 however unrealized and is only being slowly approached through inter- 

 national discussion. 



Many debatable problems are involved in classification, ranging from 

 the purely philosophical to the purely historical, and there is no part of 

 biological science in which personal judgment has greater scope or where, 

 in consequence, there is less fixity or agreement. The subject has therefore 

 a powerful appeal to the reflective mind. 



To start with, our whole attitude towards classification will depend on 

 how we answer the question whether classification is a subjective, human 

 construction or whether it exists objectively in Nature and we are trying to 

 uncover it. At the one extreme we have the view that classification origi- 

 nates in the human need for simplifying the immense diversity of Nature, 

 by grouping and relating individual objects within a logical framework, to 

 enable our limited powers to cope with them. Classification, thus viewed, 

 is a basic scientific necessity and biological classification is only one aspect 

 of this universal need. Under such a conception classification is an 

 artificial construction, unknown to Nature, and to be formed and 

 judged mainly on the principle of expediency. At the other extreme 

 is the ideal of a perfectly natural system which will express exactly the 

 evolutionary relationships of all organisms, that is to say a truly phylo- 

 genetic system which can be discovered through increased knowledge of the 

 processes and the history of evolution. These mutually exclusive views 

 are not often proposed in all their rigour, and even when they are, practical 

 considerations have generally compelled some compromise. For example, 

 those who support the second idea may display a practice which is more 

 logicallv concordant with the first theory. The result of these inconsistencies 



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