Fig. 781.—Umbel.
Fig. 782.—Capitulum or ball.
1. (1) The spike (fig. 777). In this form of inflorescence, sessile or short-stalked flowers are arranged along the rachis in the axils of the bracts; the spike is said to be compound when small spikes or spikelets arise again from the bracts of the secondary axis. (2) The catkin or amentum (fig. 777 [2]); a spike, usually pendulous, which falls off, rachis and all, by an articulation, as in the willow or hazel. 3. The spadix, a thick fleshy spike (fig. 777 [3]); examples, arum and calamus. 4. The cone, a fruit-bearing spike, covered with scales (fig. 777 [4]); examples, the coniferæ. 5. The raceme or cluster, a spike with the flowers on longer pedicels (fig. 778); examples, the currant. 6. The panicle, a branching raceme (fig. 779, Yucca gloriosa). 7. The thyrsus, a dense panicle, with longer peduncles in the middle than at the extremities; example, lilac. 8. The corymb, a raceme, in which the lower flower stalks are elongated and raised to nearly a level with the upper (fig. 780)—example, cerasus mahaleb. 9. The compound or branching corymb, a corymb in which the secondary axis again sub-divides; example, Pyrus terminalis. 10. The umbel: in this form the primary axis is greatly depressed, and the peduncles arise from a common point, and spread out like radii of nearly equal length, a whorl of bracts (involucre) surrounding the common base. In the compound umbel (fig. 781), Daucus carota, the secondary axis ends in small umbels surrounded by bracts, which is termed an involucel. This is observable in the umbelliferous plants—carrot, parsley, hemlock, etc.
Fig. 783.—Inflorescence.
A very peculiar kind of inflorescence, which characterises the great family of the compositæ, is illustrated by fig. 783. We see here the enlarged floral axis or receptacle, a, surrounded by several whorls or bracts, b b, which constitute a general involucre; the membranous bracts, (paleæ), b´ b´, seen in the receptacle, bear in their axils the sessile florets, c and d, which either have a calyx, e e, or not. The florets on the receptacle are either all of them tubular (d) or ligulate (tongue or strap-shaped); florets (c) are associated with the tubular ones. The receptacle is not always flat, but frequently presents a convex, globular, conical, concave, etc., shape.
In the absence of paleæ the receptacle is said to be naked. The florets at the margin, or circumference, are termed marginal flowers, or flowers of the ray; the florets in the disc (centre), central flowers, or flowers of the disc.
Some plants bear male and female flowers on the same stem. These are termed monæcious plants. The oak is an instance. The diæcious plants are those which bear stamens and pistil, or separately, on different plants, like willows. We will now glance at the functions of the stamens and pistil. The ovule has been mentioned as a tiny body in the ovary, and it consists of a nucleus, and cellular tissue surround it, leaving a small hole called the micropyle, into which the pollen tube enters after passing through the ovary. As in the animal creation, the unions of different families succeed best; no close relationship will fertilize so well as with other flowers.