April, 1906.] The Classification of Plants. III. 513 



THE CLASSIFICATION OF PLANTS. III. 



John H. Schaffner. 



In a natural system of classification, plants are grouped ac- 

 cording to their supposed relationships. Some groups have re- 

 semblances which leave little doubt as to the affinities of its mem- 

 bers. Each subkingdom has a number of such groups. These 

 greatest groups in the subkingdom are called classes. A class 

 may then be defined as a group of plants in a subkingdom, the 

 members of which show an evident relationship to one another 

 because of similarity of morphological and physiological char- 

 acters. This relationship must apparently be closer among the 

 members of the group than to any other member in the sub- 

 kingdom. The relationship of the class to other classes in the 

 subkingdom is in many cases indeterminable at present, or at 

 least so obscure that it gives rise to numerous disagreements 

 among systematists. This obscurity indicates that most of the 

 classes were segregated in primitive times, probalby before they 

 had passed from the condition of the next lower subkingdom 

 or stage of development. Thus classes and subclasses represent 

 more or less parallel lines of development in the same stage of 

 evolution. The class is not to be extended beyond one sub- 

 kingdom, even though its missing links be found or generally 

 assumed. Mere similarity of superficial morphological charac- 

 ters is, however, not sufficient to establish relationship ; for as is 

 well known, the same evolutionary tendencies may be operative 

 in entirely distinct groups and bring about quite similar mor- 

 phological results. The mere acquisition of some peculiarity 

 or the loss of another can not be regarded as of any special im- 

 portance in establishing a class. For example, it might turn 

 out in the future that some Conifers or Angiosperms possess 

 motile spermatozoids. But this peculiarity might persist in any 

 of the higher groups and in itself could be of no importance in 

 classification. All possible morphological characters must be 

 taken into consideration in establishing a class, due weight being 

 given to the possibilities and impossibiliites of derivation, for 

 each structure involved, from its supposed ancestral type. Quite 

 commonly relationships are claimed between groups where the 

 derivation of the one from the other involves an improbable or 

 impossible modification of the parts, and a profound credulity 

 is required before assent to the proposition is possible. Unfor- 

 tunately we are still far from possessing the necessary general 

 knowledge of plant structures and developments to make a defi- 

 nite disposition of the larger groups. It is evident that there 

 must continue to be considerable diversity of opinion as to the 

 number and limits of plant classes. Yet properly compre- 



