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 necessarv 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- 
