Classification and Nomenclature. 47 



initio, creavit infinitum ens."* Various definitions have been given 

 to species, but none accord with the actual practice of systematists 

 who seem inclined to make a species what they choose, and, in- 

 deed, the existence of various connecting forms between many 

 species distinct under normal conditions, makes the practical 

 definition of the term almost an impossibility. We may, how- 

 ever, for practical purposes, regard as a species an assemblage of 

 individuals not differing essentially from each other, and capable 

 of producing like individuals by the ordinary processes of repro- 

 duction. A recent writer defines species as " the present aspect 

 of a line of organic development, destined to become something 

 else in the future, as it was something else in the past." f This 

 would seem to be in accordance with the now widely accepted 

 biological doctrine respecting the origin of species. 



Species among ferns are founded chiefly on differences in the 

 cutting of the fronds and their method of venation. 



91. Variaties. Many forms differing only slightly from the 

 ordinary specific types, and yet capable of transmitting their 

 variations from generation to generation, are regarded as vari- 

 eties. There is a tendency on the part of a few authors to multi- 

 ply varieties indefinitely, and of a single species as many as 

 sixty-five varieties have been described. Among the be.st sys- 

 tematists, however, there is a growing tendency to restrict the 

 number. In the present volume a distinction is made between 

 those varieties that are more decided and constant in their 

 characters, and those that are more directly connected with the 

 typical forms. The former are printed in the same full-face type as 

 the species, the latter in small capitals. It would seem that the 

 latter class might as well be dropped from our lists, and possibly 

 some forms now regarded as true varieties will be found to be 

 based on characters that are not constant. 



92. Genera. The genera of ferns are founded mostly on the 

 arrangement of the sporangia on the veins, as well as the 

 character, shape, and position of the indusia. 



93. Tribes. Genera are collected into tribes, according as 

 they agree in the position and arrangement of the sporangia in 

 clusters or sori, or resemble each other in mode or habit of 

 growth. 



* There are as many different species as the Iniinlte Being created in the beginning. 

 t Dr. A. Winchell in Preadamites, p. 232. 



