470 -~ The American Naturalist. -[June, 
becamg the age of Gymnosperms. Vegetation had come upon 
a new battle-field, the terrestrial forest-ground, and only the 
- most highly organized types of preceeding ages were fitted to 
enter the struggle. Many of the Tree-Ferns and Equisetums 
were still powerful, but the supreme dominion passed over to 
the Conifers and their allies, the Cycads. The great forests of 
Conifers had their undergrowth and their tension-lines, and 
here the development of new types was progressing with prob- 
ably even greater activity than in the tension-floras of earlier 
times. The greater complexity of the conditions confronting 
a terrestrial flora over those confronting a swamp flora would 
necessarily mean more elaborate specialization. While the 
ancient coniferous tree-forms were mounting to the fulness of 
their power the first types of the higher flowering-plants were 
beginning to appear; and with the opening of the later 
Mesozoic, the Cretaceous, two new groups of tree-life came 
upon the stage as worthy competitors of the old established 
Gymnosperms. One was the order Palmacee, representing the 
Monocotyledonous Angiosperms; the other was the amenta- 
ceous hardwood tree-families, representing the Dicotyledons. 
The opening chapter in the history of these two groups is à 
matter of peculiar interest. j 
It is probable that the two groups were almost, if not quite, 
synchronous in their rise; though there is some reason to 
believe that the Palmaceæ, or at least their forerunners, the 
Pandanacez, are slightly the older. As has been indica 
the central strength of the Mesozoic foresis was undoubtedly 
held by the coniferous trees; and probably by far the greatest 
strength was vested in the near allies of the Cypresses, P mP 
-and Firs,—representing the tribes Cupressineæ, Taxodieae, 
Abietineæ, and possibly also Araucarieæ,—while the older sub- 
order Taxineæ, the broad-leaved Conifers of the Yew family, 
_ were rather crowded out toward the tension-line margins along 
. with the Cycads and Tree-Ferns. Among these last the im 
low-growing Tree-Palms probably rose, as the products ofa 
long course of elaborate specialization. It is more than pos : 
_ sible that the Pandanacew represent at least in part @ trapt : 
_ tional stage between some of the higher Gymnospermsand the a 
