5i6 



The Ohio Naturalist. 



[Vol. VI, No. 6, 



group, leads us far back into the uncertain mists of earliest 

 geological time, and into the similar mists of embryonic homo- 

 geneity. It is impracticable in the present stage of science to 

 trace the evolutionary history of classes." 



In some cases a class may fall into two or more well defined 

 subordinate groups which are quite distinct and still show an 

 evident relationship. These are called subclasses. The general 

 subgroups of a class or subclass are the orders; the orders divide 

 up into suborders and families ; the families into subfamilies and 

 genera; and the genera into species. The species may also be 

 made up of subgroups which are at present still imperfectly 

 understood and defined. 



Phyla, classes, orders, and families and other subordinate 

 groups then represent branches of closer and closer relationships, 

 shown by similarities of essential structures and produced by 

 segregation as the result of diversity of evolution and destruction 

 of intermediate types; while series and subkingdoms stand for 

 horizons or progressive stages of the evolution of the plant 

 kingdom. 



The main groups of plants rank as follows : 



Groups representing stages \ Series 



of progressive evolution. / Subkingdom. 



Groups representing phy- 

 logenetic relationships. 



Phylum 



Class 



(Subclass) 

 Order 



(Suborder) 

 Family 



(Subfamily) 

 Genus 

 Species. 



The orders are always to end in ales and the families in aceae. 

 Definite endings should also be adopted for the classes, suborders, 

 and subfamilies. 



In the accompanying diagram all classes and subclasses 

 recognized by the writer are given with their approximate re- 

 lationship indicated by the branchings of the "tree." It was 

 thought best not to attempt to indicate any definite relationships 

 between the higher Algae and Fungi although some authors have 

 in the past presented such schemes some of which may have 

 more or less merit. In a future paper the classes given will be 

 briefly defined in their proper order. 



