THE FLOWERING PLANTS. 109 
closely related to the Selaginella of the present day, have 
been the direct progenitors of the Phanerogamia. 
On account of its anatomical structure and its embryo- 
logical development, the sub-kingdom of the Phanerogamia 
has for a long time been divided into two large branches, 
into the Gymnosperms, or plants with naked seeds, and the 
Angiosperms, or plants with enclosed seeds. The latter are 
in every respect more perfect and more highly organized 
than the former, and developed out of them only at a late 
date during the secondary period. The Gymnosperms, both 
anatomically and embryologically, form the transition group 
from Ferns to Angiosperms. 
The lower, more imperfect, and the older of the two main 
classes of flowering plants, that of the Archispermee, or 
Gymnosperms (with naked seeds), attained its most varied 
development and widest distribution during the mesolithie 
or secondary epoch. It was no less characteristic of this 
period, than was the fern group of the preceding primary, 
and the Angiosperms of the succeeding tertiary, epoch. 
Hence we might call the secondary epoch that of Gymno- ° 
sperms, or after its most important representatives, the era 
of Pine Forests. The Gymnosperms are divided into three 
classes: the Coniferze, Cycadez, and Gnetacez. We find 
fossil remains of the pines, or Conifers, and of the Cycads, 
even in coal, and must infer from this that the transition 
from scaled ferns to Gymnosperms took place during the 
Coal, or possibly even in the Devonian period. However, 
the Gymnosperms play but a very subordinate part during 
the whole of the primary epoch, and do not predominate 
over Ferns until the beginning of the secondary epoch. 
Of the two classes of Gymnosperms just mentioned, that 
