and V. Opulus-the hairiness of the former and the smoothness of the latter; on the lobed form of the leaf in the latter; and, lastly, on the presence of the honey-glands and the peculiar stipuliform appendages in V. Opulus, neither of which occur in V. Lantana. In support of the above suggestions I may refer to the interesting analogy afforded-in a totally different family-by the genus Spirea. Here we find some species with entire, some with pinnate leaves; while those of S. opulifolia, as the name denotes, closely resemble those of Viburnum Opulus. Now the entireleaved species of Spiraa, like those of Viburnum, have no stipules; while Spiraea opulifolia agrees with Viburnum Opulus not only in the shape of the leaves, but in the mode of folding in the bud, and also in the presence of subulate, acuminate, stipuliform appendages. I might give other cases, but the above will, I think, be sufficient. It seems clear that the answer which we had provisionally arrived at from a study of the Rock Roses is fully borne out by the examination of other families, and that when the bud needs protection and the petiole is narrowed, this function is performed by the stipules; while, when there are no stipules, the bud is protected in some other way, and generally by the widened base of the leaf-stalk. But though the protection of the bud is the general, it is, as we shall presently see, by no means the only function which stipules perform in the economy of plants. CHAPTER III ON THE DEVELOPMENT OF LEAVES AND STIPULES IN order to arrive at a satisfactory view as to the structure and arrangement of buds it is necessary to study the development of the leaf. Steinheil (4), in 1837, was the first who approached the consideration of the subject in this rational manner; and we are also in FIG. 58.-GROWING-POINT AND BEGINNING OF FIRST LEAF OF ROSE. Highly magnified. S, apex of growing-point; B, youngest leaf; R, cortex; M, pith. debted for excellent memoirs and observations to De Mercklin (5) in 1846, Trecul (6) in 1853, Schacht (7) in 1854, Eichler (8) in 1861, Goebel (9), and others. Speaking generally, we may say that a leaf commences as a small conical projection immediately below the growing-point of the shoot (fig. 58). It continues to grow at its apex for a short time only, its develop ment being completed by growth in a zone of cells situated just above its base (intercalary growth). So that, as Schleiden has pointed out, while the apex is the youngest part of the shoot, it is the older part of the leaf. The projection gradually widens, and often occupies more than half the circumference, thus affording a possible explanation of the fact that, while the cotyledons are opposite, the leaves are in so many cases alternate. The rudimentary leaf consists of undifferentiated cellular tissue, and does not at first contain any vessels. It is no part of my present intention to deal with this interesting subject in detail, but I will give a few cases in illustration, taking that of ordinary foliage leaves, for in those which are intended as bud-protectors the stages are very different. AUCUBA On account of its simplicity, I will commence with the common Aucuba japonica of our shrubberies. The leaves of Aucuba are opposite, ovate, and without stipules. They commence as two slight projections, each of which broadens at the base, and finally occupies onehalf of the circumference of the stem (figs. 59, 60), so that they are concave on the inner side and almost cover over the growing-point. They gradually elongate (fig. 61), and from being at first slightly curved round the stem, become folded lengthways or conduplicate. They are clothed with long, sparse hairs, and show a few teeth, or rather knobs, along the edge, one terminating each of the veins, which are thicker than in subsequent stages (fig. 63). The teeth, or AUCUBA JAPONICA. Highly magnified. FIG. 59, first pair of leaves, front view; FIG. 60, ditto, side view; FIG. 61, second pair; FIG. 62, ditto, more developed; FIG. 63, third pair. knobs, are also much larger in proportion than in the full-grown leaf. COMMON LAUREL The subjoined figures illustrate the structure of the bud of a Common Laurel (Cerasus Laurocerasus). Here again the leaf commences as a small projection or lobe immediately below the growing-point. Very soon FIGS. 64-70, leaves and their stipules; s, s, stipules; x 10. two other lobes appear at the base of the first (fig. 64, s,s). These are the stipules. They are at first much smaller E |