This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
Leaf-buds consist of rudimentary leaves surrounding a growing vital point, which lengthens upwards and produces leaf after leaf upon its surface, and appear like a collection of scales arranged symmetrically one above the other. These scales are rudimentary leaves, and the centre over which they are placed, or the growing point, is a cellular substance coated with a thin stratum of spiral vessels; and these two parts answer to the pith and medullary sheath in Exogens : a very excellent example is found in the garden Asparagus (young shoots), which is Endogenous. Leaf-buds which are formed among the tissue of plants, subsequently to the development of the stem and leaves, and without reference to the latter, are called latent, adventitious, or abnor Trial. Adventitious leaf-buds may be produced from any part of the medullary system, or wherever cellular tissue is present. Leaf-buds universally originate in the horizontal or cellular system, and are formed in the root, among the wood, and at the margin or on the surface of leaves, whether perfect or rudimentary. Regular or normal leaf-buds are only found in the axils of leaves, where they exist in a developed or undeveloped state.
Practically speaking, leaf-buds are the means which nature has provided for supplying shrubs and trees with leaves and branches in autumn. Deciduous trees lose their leaves; but in the axil of each a little bud previously forms, from which fresh leaves are to expand the following spring. During winter the bud is enveloped in numerous imperfect leaves or scales, which are imbricated - that is, laid over one another like the tiles of a house. This envelope is termed hybernaculum, because it serves for the winter protection of the young and tender portions of the buds. The scales, though generally thin, are of a close membraneous texture, well suited to exclude the cold : in many cases they are also covered with a kind of gum. With the return of spring, when the sap becomes heated, or rather when the sap becomes faster in its circulation, the scales open and roll back, or in some cases fall off, to allow of the expansion of the true leaves that lie within them, curiously folded up round a kind of stem called the axis or growing point, which, as the leaves unfold, gradually elongates, and finally becomes a branch.
In the Beech and Lime the outer scales of the leaf-buds are brown, thin, and dry; in the Willow and Magnolia they are downy; in the Horse-chestnut and the Balsam Poplar they are covered with a gummy exudation.
Flower-buds are produced in a similar manner to those described above, from which they differ chiefly in containing one or more incipient flowers within the leaves - the flowers being wrapped up in their own floral leaves, or bracts, within the ordinary leaves, which have their outer covering of scales. The growing-point is generally developed when the leaves expand, but it is short and stunted, and unlike the branches produced from the leaf-buds. Every flower-bud, as soon as formed in the axil of the old leaf, contains within itself all the rudiments of the future flowers. If a bud be gathered from a Lilac or Horse-chestnut very early in spring, all the rudiments of the future leaves and flowers will be found within it, though the bud itself may not be more than half an inch long, and the flowers not bigger than the points of the smallest pins. W. Roberts.