in each stem and leaf the two are repeated. A calla, consisting of
a single straight and rigid spadix embraced by a soft and tenderly
curved spathe, affords an almost perfect expression of the
characteristic differences between Yo and In and their reciprocal
relation to each other. The two are not often combined in such
simplicity and perfection in a single form. The straight, vertical
reeds which so often grow in still, shallow water, find their
complement in the curved lily-pads which lie horizontally on its
surface. Trees such as pine and hemlock, which are excurrent--those in
which the branches start successively (i.e., after the manner of time)
from a straight and vertical central stem--are Yo; trees such as
the elm and willow, which are deliquescent--those in which the trunk
dissolves as it were simultaneously (after the manner of space) into
its branches--are In. All tree forms lie in or between these two
extremes, and leaves are susceptible of a similar classification. It
will be seen to be a classification according to time and space,
for the characteristic of time is _succession_, and of space,
_simultaneousness_: the first is expressed symbolically by elements
arranged with relation to axial lines; the second, by elements
arranged with relation to focal points (Illustrations 6,7).

The student should train himself to recognize In and Yo in all
their Protean presentments throughout nature--in the cloud upon the
mountain, the wave against the cliff, in the tracery of trees against
the sky--that he may the more readily recognize them in his chosen
art, whatever that art may be. If it happens to be painting, he will
endeavor to discern this law of duality in the composition of every
masterpiece, recognizing an instinctive obedience to it in that
favorite device of the great Renaissance masters of making an
architectural setting for their groups of figures, and he will