514 The Ohio Naturalist. [Vol. VI, No. 6, 



hended, 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 phvlogenetic 

 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 ph3dum then represents one of the, 

 great fundamental branches of the plant kingdom and consists 

 of a number of classes supposed to be inore closely related to one 

 another than to other classes. The Angiosperms are no doubt 

 such a phylum. They are not olily 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 history, 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 



