Some seeds are carried by animals; either as food such as most edible fruits and seeds,

acorns, nuts, apples, strawberries, raspberries, blackberries, plums, grasses, etc.— or invol untarily, the seeds having hooked hairs or processes, such as burrs, cleavers, etc.

Some seeds are scattered by the plants themselves, as, for instance, those of many Geraniums, Violets, Balsams, Shamrocks, etc. Our little Herb Robert throws its seeds some 25 feet.

Some seeds force themselves into the ground, as those of certain grasses, Cranes'bills (Erodiums), etc.

Some are buried by the parent plants, as those of certain clovers, vetches, violets, etc.

Some attach themselves to the soil, as those of the Flax; or to trees, as in the case of the Mistletoe.

LEAVES

Again, as regards the leaves there can, I think, be no doubt that similar considerations

of utility are applicable. Their forms are almost infinitely varied. To quote Ruskin's vivid words, they "take all kinds of strange shapes, as if to invite us to examine them. Star-shaped, heart-shaped, spear-shaped, arrowshaped, fretted, fringed, cleft, furrowed, serrated, sinuated, in whorls, in tufts, in spires, in wreaths, endlessly expressive, deceptive, fantastic, never the same from foot-stalk to blossom, they seem perpetually to tempt our watchfulness and take delight in outstepping our wonder."

But besides these differences of mere form, there are many others of structure, texture, and surface; some are scented or have a strong taste, or acrid juice, some are smooth, others hairy; and the hairs again are of various kinds.

1

I have elsewhere 1 endeavoured to explain some of the causes which have determined these endless varieties. In the Beech, for instance (Fig. 15), the leaf has an area of about 3 square inches. The distance between the buds is about 1 inch, and the leaves lie in

1 Flowers, Fruits, and Leaves.

the general plane of the branch, which bends slightly at each internode. The basal half of

the leaf fits the swell of

the twig, while the upper half follows the edge of the leaf above; and the form of the inner edge being thus determined, decides that of the outer one also.

The weight, and consequently the size of the leaf, is limited by the strength of the twig; and, again, in a climate such as

ours it is important to plants to have their leaves so arranged as to secure the maximum of light. Hence in leaves which lie parallel to the plane of the boughs, as in the Beech, the width depends partly on the distance between the buds; if the leaves were broader, they would overlap, if they were narrower, space would be wasted. Consequently the width being determined by the distance between the buds, and the size depending on the weight

which the twig can safely support, the length also is determined. This argument is well illustrated by comparing the leaves of the Beech with those of the Spanish Chestnut. The arrangement is similar, and the distance between the buds being about the same, so is the width of the leaves. But the terminal branches of the Spanish Chestnut being much stronger, the leaves can safely be heavier; hence the width being fixed, they grow in length and assume the well-known and peculiar sword-blade shape.

In the Sycamores, Maples (Fig. 16), and Horse-Chestnuts the arrangement is altogether different. The shoots are stiff and upright with leaves placed at right angles to the branches instead of being parallel to them. The leaves are in pairs and decussate with one another; while the lower ones have long petioles which bring them almost to the level of the upper pairs, the whole thus forming a beautiful dome.

For leaves arranged as in the Beech the gentle swell at the base is admirably suited; but in a crown of leaves such as those of the

Sycamore, space would be wasted, and it is better that they should expand at once, so soon as their stalks have carried them free from the upper and inner leaves.

In the Black Poplar the arrangement of the leaves is again quite different. The leaf stalk is flattened, so that the leaves hang

Fig. 16. Acer platanoides.

vertically. In connection with this it will be observed that while in most leaves the upper and under surfaces are quite unlike, in the Black Poplar on the contrary they are very similar. The stomata or breathing holes, moreover, which in the leaves of most trees are confined to the under surface, are in this species nearly equally numerous on both.