284. The speaker's purpose was to exhibit the development of the common forms of branch, in dicotyledonous trees, from the fixed type of the annual shoot. Three principal modes of increase and growth might be distinguished in all accumulative change, namely:—

1. Simple aggregation, having no periodical or otherwise defined limit, and subject only to laws of cohesion and crystallization, as in inorganic matter.

2. Addition of similar parts to each other, under some law fixing their limits and securing their unity.

3. Enlargement, or systematic change in arrangement, of a typical form, as in the growth of the members of an animal.

285. The growth of trees came under the second of these heads. A tree did not increase in stem or boughs as the wrist and hand of a child increased to the wrist and hand of a man; but it was built up by additions of similar parts, as a city is increased by the building of new rows of houses.

Any annual shoot was most conveniently to be considered as a single rod, which would always grow vertically if possible.

Every such rod or pillar was, in common timber trees, typically either polygonal in section, or rectangular.

If polygonal, the leaves were arranged on it in a spiral order, as in the elm or oak.

If rectangular, the leaves were arranged on it in pairs, set alternately at right angles to each other.

Intermediate forms connected each of these types with those of monocotyledonous trees. The structure of the arbor vitÆ might be considered as typically representing the link between the rectangular structure and that of monocotyledons; and that of the pine between the polygonal structure and that of 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 expansion (under fixed mechanical conditions) by light, heat, moisture, etc. But vegetable tissue in the living branch did not contract nor expand under external influence alone. The principle of life manifested itself either by contention with, or felicitous recognition of, external force. It accepted with a visible, active, and apparently joyful concurrence, the influences which led the bough towards its due place in the economy of the tree; and it obeyed reluctantly, partially, and with distorted curvatures, those which forced it to violate the typical organic form. The attention of painters of foliage had seldom been drawn with sufficient accuracy to the lines either of branch curvature, or leaf contour, as expressing these subtle laws of incipient volition; but the relative merit of the great schools of figure design might, in absence of all other evidence, be determined, almost without error, by observing the precision of their treatment of leaf curvature. The leaf-painting round the head of Ariosto by Titian, in the National Gallery, might be instanced.

289. The leaf thus differed from the flower in forming and protecting behind it, not only the bud in which was the form of a new shoot like itself, but a piece of permanent work, and produced substance, by which every following shoot could be placed under different circumstances from its predecessor. Every leaf labored to solidify this substance during its own life; but the seed left by the flower matured only as the flower perished.

This difference in the action and endurance of the flower and leaf had been applied by nearly all great nations as a type of the variously active and productive states of life among individuals or commonwealths. Chaucer's poem of the "Flower and Leaf" is the most definite expression of the mediÆval feeling in this respect, while the fables of the rape of Proserpine and of Apollo and Daphne embody that of the Greeks. There is no Greek goddess corresponding to the Flora of the Romans. Their Flora is Persephone, "the bringer of death." She plays for a little while in the Sicilian fields, gathering flowers, then snatched away by Pluto, receives her chief power as she vanishes from our sight, and is crowned in the grave. Daphne, on the other hand, is the daughter of one of the great Arcadian river gods, and of the earth; she is the type of the river mist filling the rocky vales of Arcadia; the sun, pursuing this mist from dell to dell, is Apollo pursuing Daphne; where the mist is protected from his rays by the rock shadows, the laurel and other richest vegetation spring by the river-sides, so that the laurel-leaf becomes the type, in the Greek mind, of the beneficent ministry and vitality of the rivers and the earth, under the beams of sunshine; and therefore it is chosen to form the signet-crown of highest honor for gods or men, honor for work born of the strength and dew of the earth and informed by the central light of heaven; work living, perennial, and beneficent.

J. R.