Fig. 13. A linear leaf with an acute tip. Fig. 14. Lanceolate leaf with an acuminate tip. Fig. 15. Oblanceolate leaf broadest above the middle. Fig. 16. Ovate, broadest below the middle. Fig. 17. Spatulate, broadest above the middle and with an elongated base. Fig. 18. Elliptical. Fig. 19. Obovate in which the general shape is ovate, but broadest toward the tip. Fig. 20. Oblong. Fig. 21. Orbicular or nearly round. Fig. 22. Deltoid or somewhat triangular, an ovate leaf with a broad base. Fig. 23. Kidney-shaped or reniform with heart-shaped base. Fig. 24. Peltate leaf of common garden nasturtium; note circular blade with leafstalk attached to the center.] types, but in nearly every case, once the difference is noted--and scarcely any other character of a plant is so much worth notice--they cannot be mistaken. During the winter nearly all leaves are folded in various ways in a bud for protection from the elements. Nature shows herself in some of her wisest moods in the selection of methods to accomplish this. In some buds, notably those of the horse-chestnut, the bud is coated with a sticky substance to protect the tender young leaves inside. In others there is a hard outer coat, as in the hickory, impregnable to the most driving sleet, others again have the leaf rolled so tightly and pointed so sharply at the end, as in the beech, that water cannot cling to the bud nor soak in, until the warmth of spring gives the signal for the annual miracle of the bursting out of foliage. Leaf buds are sometimes hard to find on certain plants, as they are formed at the base of a leafstalk and covered by it during the growing season. It is only as the leaf falls in the autumn that the hollow base of its stalk is seen to have hidden during the summer the young bud for the following season. The plane tree or sycamore is a good example of a plant where no leaf buds can be found until the falling of the leaves in autumn. The forms of leaves are infinite in their variety, and the reasons for some of their peculiarities in this respect are not yet understood. The average netveined leaf is obviously composed of a _blade_ (Figure 25), and at the base a stalk known as a _petiole_. Sometimes at the base of the petiole--which is lacking in many leaves--there are two tiny leaflike appendages, called _stipules_, which are of no apparent use to the plant, and, as if in recognition of this fact, they often fall off long before autumn. In some plants, however, stipules are permanent, while in certain others they are never found, as, for instance, in the horse-chestnut tree. [Illustration: FIGS. 25-35.--FORMS AND BASES OF LEAVES