PART IV. 

 CLASSIFICATION. 



Introductory. A systematic classification of plants may be 

 arrived at by either of two methods. In the first, the different 

 forms of plants are arranged according to some one given prin- 

 ciple ; by this means order is established, and a definite position 

 in the system is assigned to each plant. Many such systems have 

 been devised, and are known as artificial systems. The principle 

 of classification in such a case must be determined more or less 

 arbitrarily and without considering whether or not, in the resulting 

 arrangement, the plants which are nearly allied are always brought 

 together, and those which are less nearly allied are kept apart. 

 The best known of these artificial systems is that of Linnseus, 

 called the sexual system, which classifies plants by the number 

 and mode of arrangement of the floral organs. This system is, 

 however, only applicable to Phanerogams. 



The natural system, to the gradual development of which a more 

 exact knowledge of the reproduction of Cryptogams has largely 

 contributed, has for its object the classification of plants according 

 to their fundamental relationships ; and as these are established 

 once for all by Nature itself, the natural system is not based upon 

 any arbitrary principle of classification, but depends upon the 

 state of our knowledge of these fundamental relationships. These 

 find their chief expression in the structure and other characteristics 

 of the reproductive organs, as well as in the peculiarities of poly- 

 morphism presented by the life-history (see p. 2). This is more 

 particularly true with regard to the definition of the larger groups 

 of the Vegetable Kingdom ; within these groups relationships may 

 be exhibited sometimes in one way and sometimes in another, so 

 that it is not possible to lay down any universal rules for deter- 

 mining closS affinities. 



As the investigation of this subject is still far from complete 



