I now come to the stipuliform appendages. These often bear honey-glands, but by no means always, and even where these occur there seems no reason why they should be situated on filiform appendages. On the whole, then, I doubt whether they can be explained as mere honey-glands, or whether, indeed, they are of any actual use when the leaves are fully developed.

When we meet with a small organ which appears to have no definite function, we naturally ask ourselves whether it is the disappearing relic of some larger organ which at one time performed some useful purpose in the economy of the animal or plant. This suggestion, however, seems untenable in the present case, because, as a matter of fact, we do not find that the stipuliform appendages are more developed in any of the species allied to V. Opulus.

There is, however, a physical cause to which, perhaps, the presence of these organs may be due. We have seen that much the larger number of species of Viburnum have entire leaves, more or less oval or ovate. This would appear to be the form typical or original to the genus.

Now let us suppose that, either from having extended northwards (and both Viburnum Lantana and V. Opulus are among the northern representatives of the genus), or from some other cause, the young leaves require additional protection. This may be effected in several ways. For instance, the young leaf may be guarded

by a thick coat of felted hairs; this is the case in V. Lantana. Another plan would be that the outer leaves should become leathery, and thus protect the inner ones; this is the case with V. Opulus. But that being so, it is an advantage that the inner or true leaves should be folded, because they thus occupy less space. This, perhaps, accounts for the folding of the

leaves of V. Opulus in the bud, while the lobes follow from the mode in which the leaves are folded. Now a leaf folded up, as are those of V. Opulus, requires only two or three lateral veins. The LL remaining veins, then, and the membrane connecting them, will gradually be reduced, and ultimately disappear.

In V. Opulus, as is shown in the figure (fig. 57), there is a space left be

VIBURNUM OPU-tween the bases of the leaves. In the

LUS, × 4.

next younger pair

of leaves; St, stipule.

L, L, lateral lobes of genus Acer, many species of which leaf; L, one of have leaves somewhat resembling those of V. Opulus, this space is fully occupied by the following pair of leaves. This, however is not the case in V. Opulus, and the space thus left unoccupied is filled up by the stipuliform appendages. I may also observe that the stipuliform appendages resemble leaf-lobes in being slightly conduplicate.

These considerations seem to throw some light on the differences between the leaves of Viburnum Lantana

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 Spiraea. 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 Spiraea, 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