f monocotyledons.

Every leaf during its vitality secreting carbon from the atmosphere,
with the elements of water, formed a certain quantity of woody tissue,
which extended down the outside of the tree to the ground, and farther
to the extremities of the roots. The mode in which this descending
masonry was added appeared to depend on the peculiar functions of
cambium, and (the speaker believed) was as yet unexplained by botanists.

286. Every leaf, besides forming this masonry all down the tree,
protected a bud at the base of its own stalk. From this bud, unless
rendered abortive, a new shoot would spring next year. Now, supposing
that out of the leaf-buds on each shoot of a pentagonal tree, only five
at its extremity or on its side were permitted to develop themselves,
even under this limitation the number of shoots developed from a single
one in the seventh year would be 78,125. The external form of a
healthily grown tree at any period of its development was therefore
composed of a mass of sprays, whose vitality was approximately
distributed over the _surface_ of the tree to an equal depth. The
branches beneath at once supported, and were fed by, this orbicular
field, or animated external garment of vegetation, from every several
leaf of which, as from an innumerable multitude of small green
fountains, the streams of woody fiber descended, met, and united as
rivers do, and gathered their full flood into the strength of the stem.

287. The principal errors which had been committed by artists in drawing
trees had arisen from their regarding the bough as ramifying
irregularly, and somewhat losing in energy towards the extremity;
whereas the real boughs threw their whole energy, and multiplied their
substance, towards the extremities, ranking themselves in more or less
cup-shaped tiers round the trunk, and forming a compact united surface
at the exterior of the tree.

288. In the course of arrival at this form, the bough, throughout its
whole length, showed itself to be influenced by a force like that of an
animal's instinct. Its minor curves and angles were all subjected to one
strong ruling tendency and law of advance, dependent partly on the aim
of every shoot to raise itself upright, partly on the necessity which
each was under to yield due place to the neighboring leaves, and obtain
for itself as much light and air as possible. It had indeed been
ascertained that vegetable tissue was liable to contractions and
e