OKGANS OF EEPEODUCTION. 



63 



345. A Head (cajpUulum) is a more or less globular 

 arrangement of the flowers, as in the Clover and the 

 Button-bush, fig. 4. Neither the primary nor secondary 

 axes are elongated in the head. This form of inflores- 

 cence is often surrounded by a cluster of bracts called 

 an involucre, as in the Marigold, fig. 1, which belongs to 

 the Order CompositEE, embracing the Compound Flowers 

 of the old Botanists. Here we find a peculiar mode of 

 inflorescence. The rachis is expanded into a broad disc, 

 called the Torus, or Receptacle, as may be seen in the 

 Dandelion, Aster, Thistle, or any of the flowers in this 

 numerous family. 



THE CENTRIFUQAL FORM. 



CHAPTER XXIV. 



0EGAN8 OF EEPEODUCTION. 



346. This is generally to be distinguished by the 

 presence of a single flower at the termination of the 

 primary axis and its forked branches. The principal 

 forms of the Centrifugal mode of inflorescence are, the 

 Cyme, Fascicle, and Verticillaster. 



347. The Cyme externally resembles an umbel in 

 the primary arrangement of its stalks, which all radiate 

 from a common centre, but differs from it in their secon- 

 dary distribution, by which they are irregularly sub- 

 divided, the branches being repeatedly two or three 

 forked, the whole forming a level, or nearly level top, as 

 in the Elder, which, however, is not very well represented 

 in fig. 8. 



348. The Fascicle is an arrangement of the Corymb, 

 in which the flowers are crowded or bundled together, as 

 in the Sweet William, fig. 3. 



349. The Vekticillasteh is the infiorescence of the 

 Mint tribe ; and though often called a whorl, it is not 

 so, since the flowers do not actually surround the stem, 

 but occupy opposite points in the axils of each pair of 

 leaves. The only true verticil, or real whorl of flowers, 

 is found in plants with whorled leaves, as the Water- 

 Milfoil. The verticillaster is seen at fig. 6. 



350. Bracteoles are the smaller bracts often found 

 on the' branches of the inflorescence; but though it is 

 often necessary to distinguish between these and those 

 that grow at the basis of the primary branches, there is 

 no absolute distinction between them, other than that of 

 position. 



351. Atypical, or complete flower, consists of the 

 Essential Organs, or the Stamens and Pistils, and their 

 Envelopes. The first are called Essential organs, be- 

 cause they are never wanting, as no flower can be per- 

 fected without them ; and the last, in their normal state, 

 coiisist of two sets of leaves, remarkably different from 

 each other in form, color, and texture. The Floral 

 Envelopes are, therefore, exterior to the stamens and 

 pistils, which in the bud they inclose, and after expan- 

 sion, shelter and protect. These are generally of two 

 kinds, occupying two distinct circles, one of which is 

 above or interior to the other. The lowest or outermost 

 of these is called the Calyx ; the upper, or inmost, the 

 Corolla. But when only one whorl is present, it is 

 classed among calyx forms, whatever may be its charac- 

 ter, and is then usually termed a Perianth {around the 

 flower). The parts or divisions of the; Calyx are termed 

 Sepals ; those of the Corolla, Petals. 



352. Occupying the next circles within the corolla, 

 come the Stamens, or Fertilizing Organs. 



353. The Pistils, one or more, stand in the centre 

 of the flower, and thus terminate its axis of growth. 

 They are inclosed by the stamens, and are called the 

 Fertile, or Seed-bearing Organs. 



354. A Complete Flower, then, consists of these 

 four whorls — the Calyx, the Corolla, the Stamens, and 

 the Pistils ; and they all, either directly or indirectly, 

 are seated on the Torus out of which they grow. 



355. Such is the structure of a complete flower; but 

 from this type there are many variations, the most im- 

 portant of which is the separation of the stamens and 

 pistils, which sometimes grow in separate flowers. In 

 the Hickory, fig. 2, the staminate flowers occupy the 

 ament a, and the solitary pistillate flower is seen in the 

 little nutlike body, with its small clusters of transformed 

 leaves, near the summit of the branch. At other times 

 they are still more widely separated, occupying not only 

 different flowers, but distinct plants, as in the Poplar, 

 Fig, Palm, and Willow trees. The symmetry of the 

 flower is also frequently destroyed by the abortion or 

 suppression of some of its parts or whorls. This often 

 happens with the calyx and corolla. 



Spike and Araont? Describe the inflorescence of the Cempositse. What 

 were the plants of this Order termed by the old Eotanists ? How is the rachis 

 in this tribe — its name ? 



General subject Of what does the Complete Flower consist ? How many 

 Florftl*nvelopos? Are they essential? What is the lowest or ontermost 

 whorl named— the next ? Name the next circle within the Corolla — ^the next. 



Which is the central whorl? Which of all these groups are essential S Define 

 stamens — their position and office — Pistils. Most important variation from 

 this type — ^how caused ? How are the stamens and pistils in the Hickory tribe 

 — in the Palm tribe ? How many whorls of Floral Envelopes in the typical 

 flower ? When bat one whorl is present, what is it called ? How many whorls 

 in all ? Name and define their true order. 



