eaflessness, a beautiful composition of line rather than of form (see
illustration, p. 143[f081b]).

[Illustration (f081b): General Principles of Line and Form in the
Branching and Foliage Masses of Trees.]

Here we see organic life and structure expressed in the vigorous spring
of inter-dependent and corresponding curves, from the rigid sinuous
column of the main stem springing from the ground, presently divided
into the main forks of the branches, which again subdivide and subdivide
into smaller forks, so that the tree may sustain and spread its life in
the air and the sun, both supporting and continuing its existence by
this wonderful economic system of co-operative, subdivided, and
graduated helpfulness.

The massive green pavilion of summer, which this delicate vaulting of
branch-work sustains, gives us another, more sumptuous, but perhaps not
a greater beauty in the combination or substitution of form and mass for
line composition.

[Form and Mass in Foliage]

We might express, in an abstract way, the principle of the
line-structure of the ramifying tree by super-imposing vertically fork
upon fork in gradually diminishing scale, either curvilinear or
rectangular; and the principle of the mass-structure in the formation of
the foliage might be expressed by a series of overlapping curves,
suggestive of scales or cloud masses: to both of which indeed they
correspond in principle, illustrating the scale principle in detail and
the cloud principle in the mass; thus repeating the same general law of
natural roofing, or covering, in different materials (see
illustration, p. 145[f082]).

[Illustration (f082): Principles of Structure in Foliage Masses.]

In a mass of foliage each leaf falls partly over the one below it, as by
the system of their growth and suspension upon the stem they are of
course bound to do, whether symmetric or alternate in their arrangement,
the gaps caused by decay or accident being generally filled by new
shoots. Each shoot, eager to expand its leaves in the light, ever
spreading, forms mass after mass of the beautiful green panoply--the
coat armour of the forest, arboreal man's first form of domestic
architecture.

[Illustration (f083): Albert Durer: Detail from 'The Prodigal Son.']

The principle of structure here is just the same as the overlapping
principle of the tiles and slates upon our ordinary house-roofs; but
each leafy tile is di