The Grouping of Vascular Plants 
89 
DESCRIPTION OF THE DIAGRAM. 
The periphery of the diagram represents the end members of three evolu¬ 
tionary series, the Haplophylls, the Meiophvlls and the Meriphylls, and, very 
roughly, their relative dominance at the present time. 
All Families that fail to reach the periphery are extinct. 
All Families outside the dotted line are spermophytes. 
The circle in the centre, which is hatched, represents the pre-land-plants 
which, after Church, we are learning to call Thalassiophyta. 
The annulus immediately surrounding this circle represents the earliest 
known vascular plants which may at present be identified with the Psilophy- 
tales of Kidston and Lang. From these proceed races with at least three types 
of appendicular, photosynthetic organs. It can be seen that the Haplophylls 
produced no seed plants; the Meiophylls are regarded as having given rise to 
the Sphenopsida, Cordaitales, Ginkgoales and Coniferse; the Meriphylls are 
the successful races, giving rise to the Ferns, the Cycadophyta, the Gnetales 
and the Angiosperms. 
