Ree a ent, Sele oe a” nD 
1894.] The Meaning of Tree-Life. 579 
Pacific strip became the refuge and stronghold during glacial 
times of the mightiest phalanx in the North American coni- 
ferous forest, and there they have stayed, simply because all 
competitors perished before their invasion. Obviously the 
conditions in the case of the Asian coniferous invasion were 
vastly different ; while the comparative poverty of the conifer- 
ous element in the Appalachian forest is directly traceable to 
the strength of its hardwood element and the path of retreat 
afforded the Conifers toward the north and northwest. 
A remarkable example of the development of higher types 
along the tensional margin-line was the glossopteris flora of the 
Carboniferous glacial regions,—a flora an age ahead of that 
of the rest of the world, and developed where the latter flora 
was beaten back by the glacial cold. 
Many details of great interest to the systematic botanist 
might be outlined in this connection, but what has been 
suggested suffices to show how vitally important is the 
chapter of plant-history recorded in the world’s tree-life. It 
will be found on comparison, that the record of the develop- 
ment and migrations of shrubby and herbaceous plants closely 
accords with the history of the tree-groups with which they 
are most closely allied. But the stability of tree characters 
vastly exceeds that of the characters of the lesser plant forms, 
and hence it is these latter that vary most in passing from 
one region to another. Still in this latitude we may clearly 
observe that the more ancient herbaceous forms are the more 
northerly in their range, and the newer the more southerly. 
The equatorial belt has become the great center of develop- 
mental activity, and out from its congested tension-margins 
come the vanguard of our highest floral types. The coniferous 
trees were all-powerful in the Mesozoic; the Hardwood trees 
of the amentaceous and choripetalous Dicotyls seem to have 
reached a climax of luxuriance in the late Tertiary; and out 
of the great element of sympetalous Dicotyls that predominate 
the herbaceous flora of the present world, there may be 
developed another great tree group that shall rule the forest 
of the far off future. The promise of this last is already to be 
found in the arborescent Composite of certain of the Pacific 
