1804] ) The Meaning of Tree-Life. 471 
Palmacew ; and it is well worthy of note that the aerial roots 
of the Screw-Pines, the Pandanacew, are a living memorial to 
the position they originally held on the shore-margin of a 
forest tension-line. The habit of growth of the Palmacez most 
strikingly suggests that their first competitors were Tree-Ferns 
and Cycads, even as they are in many regions to-day. It seems 
as ifthe first Palms had met the Mesozoic Tree-Ferns and 
Cycads on their own ground,—the forest margin,—with their 
own weapons—the tall aspiring trunk topped with a crown of 
leaves. And by their general higher character of organization 
the Palms ultimately asserted their preeminent superiority. 
The wide constrast between the floral characters of the Palm- 
aceæ and those of the Gymnosperms presents a difficult prob- 
lem. There is a strong likelihood, however, that the spadice- 
ous inflorescence of the Screw-Pines and Palms is a highly 
specialized development from the cones of some aberrant 
Cycad or Conifer. At least all the probablities indicate that 
the spadiceous Monocotyls approach much nearer the Gymno- 
sperms than do any of the non-spadiceous ones. All this has 
evidently a most significant bearing on the question before us, 
of the Palms’ place in Nature. We have seen that the vegeta- 
tive character of the Palms was widely different from that of 
the dominant Conifers; and now we note that their floral 
organs were also widely different, and in fact far more decidedly 
unlike the cones of the Cypresses and Pines than are the “ cat- 
_ kins” of the hardwood dicotyl trees. 
There are a half-dozen or more tree-orders among the Dico- 
tyls that should really stand apart as forming a small sub- 
class quite decidedly distinct from the rest of the Dicotyls. As 
the principal orders of this group may be named the Juglan- 
aceæ, Myricacez, Salicaceæ, Betulaceæ, Fagacex, Ulmacez, 
Platanaces, and a couple of others. These have been called 
the Amentaceze, or the Dicline, and might be regarded as a 
subclass. Except in the approach of Ulmacew to the Urtica- 
ceæ, the Diclinæ stand clearly apart as a distinctive highly 
Specialized alliance of trees and shrubs. Their relation to 
re Mesozoic Gymnosperms is an interesting question. In 
general habit of growth and in the character of their wood 
they evidently make a close approach to the Confers. 
