[Illustration: MARGINS OF LEAVES 1. Entire. 2. Serrate or sawlike. 3. Doubly serrate. 4. Dentate or toothed. 5. Crenate. 6. Doubly crenate. 7. Sinuate or wavy.] It is not necessary to describe separately all the principal forms of simple and compound leaves. These are illustrated, and the student should either make himself acquainted with the terms applied to the different shapes, or refer, as occasion requires, to the illustrations. Concerning the compound leaves, however, their segments are themselves sometimes divided after the manner of the whole, and even the secondary segments may be similarly cut. Thus, if the segments of a pinnate leaf are themselves pinnately compound, the leaf is said to be _bi-pinnate_; and, if the secondary segments are also compound, it is a _tri-pinnate_ leaf. INFLORESCENCE We must now turn our attention to the different kinds of _inflorescence_ or arrangement of flowers. Flowers are commonly mounted on stalks (_peduncles_), but in many cases they have no stalks, being attached directly to the stem of the plant, and therefore said to be _sessile_. Whether stalked or sessile, if they arise from the axils of the leaves--the angles formed by the leafstalks and the stem--they are said to be axillary. When only one flower grows on a stalk it is said to be _solitary_; but in many cases we find a number of flowers on one peduncle, in which instances, should each flower of the cluster have a separate stalk of its own, the main stalk only is called the peduncle, and the lesser stalks bearing the individual flowers are the _pedicels_. [Illustration: VARIOUS FORMS OF SIMPLE LEAVES 1. Oval or elliptical. 2. Ovate. 3. Obovate. 4. Orbicular. 5. Lanceolate. 6. Linear. 7. Cordate (heart-shaped). 8. Obcordate. 9. Reniform (kidney-shaped). 10. Sagittate (Arrow-shaped). 11. Rhomboidal. 12. Spathulate (spoon-shaped). 13. Peltate (stalk fixed to the centre). 14. Oblique. 15. Runcinate (lobes pointing more or less downwards). 16. Hastate (halberd-shaped). 17. Angled. 18. Palmate. 19. Pinnatifid.] [Illustration: FORMS OF COMPOUND LEAVES 1. Binate. 2. Ternate. 3. Digitate. 4. Pinnate.] [Illustration: FORMS OF INFLORESCENCE 1. Spike. 2. Raceme. 3. Corymb. 4. Umbel. 5. Cyme. 6. Compound Raceme or Panicle. 7. Capitulum or Head. 8. Compound Umbel.] It is often convenient to make use of certain terms to denote the various arrangements of flower-clusters, and the principal of these are as follows:-- 1. _Spike._--Sessile flowers arranged along a common axis. 2. _Raceme._--Flowers stalked along a common axis. 3. _Corymb._--Flowers stalked along a common axis, but the lengths of the pedicels varying in such a manner as to bring all the flowers to the same level. 4. _Umbel._--The pedicels all start from the same level on the peduncle. 5. _Cyme._--An arrangement in which the flower directly at the end of the peduncle opens first, followed by those on the branching pedicels.