1894.] The Meaning of Tree-Lafe. 469 
The history of plant-life through the later Silurian and the — 
Devonian Age records the first strong establishment of a truly 
dry-land flora, a substantial foreshadowing of the Mesozoic. 
The changes in physical conditions of course furthered this 
i result no less truly than did the adaptive evolution of organic 
forms. In the dry-land forests of the Devonian rose the vege- 
tation whose future developments should hold dominion when 
the primordial swamps had disappeared from the earth. But 
these terrestrial forests evidently had the effect of removing an 
immense part of the pressure upon the old swamp-jungles by 
: becoming the main refuge and stronghold of the new types 
crowded out at the old tension-line. This, together with the 
physical changes recorded im the rock-systems of the 
i times, gave full vent to the gathering vegetative energy that 
reached such a stupendous culmination in the mammoth 
swamp-flora of the Coal Age. Here was a turning point in 
plent-history. With the dawn of the Mesozoic came the clear 
prophecy of modern conditions. The dry-land forests of the 
: Reptilian Age were the full realization of the conditions fore- 
a shadowed in the Devonian. Out of the swamp-forests of the 
7 Carboniferous came some of the highest Lycopods, great Tree- 
eee 
Ferns, and giant Equisetums. Down from the Devonian came 
the Conifers of the yew-family; and as reminders of the old 
genus Cordaites the new order Cycadacew appeared. Un- 
doubtedly it is impossible to believe that the swamp-flora of 
the coal seams represents anything like the whole flora of the 
Carboniferous Age. There must of necessity have also existed 
then a great transitional dry-land flora between the terrestrial 
forests of the preceeding Devonian and- the succeeding Jura- 
rias. Much of the strata called Devonian or Mesozoic prob- 
ably represents this transition and was synchronous 1n its 
formation with the accumulation of the coal. Part of the 
transition is clearly observable in the nonearboniferous forma- 
tions included between the coal-seams. While the prep- 
_ arations, begun in the Devonian, for the great Mesozoic forests 
_ were slowly and surely progressing, the old vegetation of the 
_ S8wamp-jungle swept up to its culmination, and marked by its 
_ decline the close of the Paleozoic Era. The early Mesozoic 
