The Ohio Naturalist. 
[Vol. VI, No. 6, 
516 
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. 
j 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. 
Groups representing phy- 
logenetic relationships. . 
