THE OLDEST PLANTS 16f 
earliest period from which plant remains are well pre- 
served and plentiful, in the Devonian rocks, many of 
the great plant groups are fully developed, the vege- 
tation displaying an abundance and luxuriance com- 
parable to that of the present day. Seaweeds (Algz), 
Horsetails (Equisetales), Ferns (Filicales), Club- 
mosses (Lycopodiales), fill the waters or clothe the 
land, and Seed Plants are already abundant in the 
form of the fern-like Pteridosperms, long since 
extinct. Both as regards adaptation to environment 
and internal structure a very high degree of speciali- 
zation has already been obtained. “If a botanist,” 
writes D. H. Scott, “were set to examine, without 
prejudice, the structure of those Devonian plants 
which have come down to us in a fit state for such 
investigation, it would probably never occur to him 
that they were any simpler than plants of the present 
day; he would find them different in many ways, but 
about on the same general level of organization.” 
In the succeeding Carboniferous Period conditions 
appear to have been peculiarly suitable for vegetable 
life, as well as for its preservation in a fossil condition. 
In the warm, moist climate of those times, many of 
the races of plants above mentioned attained an im- 
posing size, luxuriance, abundance, and variety; and 
their remains, fortunately well preserved owing to 
conditions favourable to slow decomposition, not 
only furnish a rich heritage for the botanist, but 
supply the coal, on the energy derived from which 
our whole modern civilization is built up. 
Before the end of the Paleozoic Period the Coni- 
fers had appeared, descended possibly from the 
extinct Cordaitee. With the advent of the Secondary 
It 
