514 
The Ohio Naturalist. 
[Vol. VI, No. 6, 
bended, the class stands out as the large unit of classification 
and with a fair knowledge of structure and function there should 
be little necessity for the shifting of species from one class to 
another. 
In some cases it is a comparatively easy matter to recognize 
the class while in others it is exceedingly difficult. In the 
Homosporous Pteridophytes there are plainly three distinct types 
of living species, lycopods, horsetails, and ferns, and these repre- 
sent the three classes of the subkingdom. Whether the ferns 
could be regarded as reprensenting more than one phylogenetic 
branch may be a question with some. The quillworts show 
characters which exclude them from both the selaginellas and 
the eusporangiate ferns. For this reason they have been shifted 
about from one place to another without finding a permanent 
home. 
Evidently in all such cases the proper procedure is to estab- 
lish a distinct class and then the arguments as to their relation- 
ship with other classes may proceed pro and con ad infinitum. 
In a general way one may recognize relationships between 
certain classes and if this is possible such a group of classes will 
constitute a phylum. A phylum then represents one of the 
great fundamental branches of the plant kingdom and consists 
of a number of classes supposed to be more closely related to one 
another than to other classes. The Angiosperms are no doubt 
such a phylum. They are not only the greatest group of plants 
but a very isolated group which appears to have come from a 
common ancient stock. The Gymnosperms are probably a poly- 
phyletic subkingdom. The Cyanophyceae, Schizomycetes, and 
Myxoschizomycetes probably represent a phylum, the Schizo- 
phyta. A phylum may extend from one subkingdom to another. 
This is probably the case with lycopods, selaginellas and their 
fossil allies. But as a general rule the relationships between 
lower and higher groups have not been definitely determined. 
Too little is known of the morphology and geological history of 
plants to make possible the establishment of phyla with any 
great certainty. 
Henry Shaler Williams, in his Geological Biology, makes the 
following important statements on this point; 
“The arrangement into branches, therefore, is from a struc- 
tural point of view highly artificial; and for purposes of tracing 
the historv, or even from a taxonomic point of view, it is of little 
importance to deal with characters more ancient or of higher 
rank than the class characters.’’ 
“ It may be convenient to associate the classes together into 
larger groups ; but to reach the point of real union of their char- 
acters, in order to associate two or more classes in a common 
