INFLORESCENCE. 



61 



330. One of the component parts of Inflorescence is 

 the Flower-stalk, which is called a PEDUNCLE. When 

 the peduncle is not present, the flower is said to be sessile. 

 This organ bears no leaves, or only BRACTS. 



331. Like the stem, of which it is a part, the peduncle 

 may be eithci simple or branched. The axis of a com- 

 pound peduncle is called the RACHIS, and may be seen in 

 the Lilac, Oat and Currant, figs. 8, 4 and 6, of Plate 

 XX. Its subdivisions are. called PEDICELS. 



332. A SCAPE is a flower-stalk that springs from a 

 subterranean stem, bearing no leaves, or only minute 

 bracts, as in the Dandelion, and many speciea of Violet. 

 Such plants were formerly called acaulescent, or STEM- 

 LESS, but no plant is now considered to be without a 

 stem. 



333. SOLITARY INFLORESCENCE is that in which the 

 cluster is reduced to its simplest form, and contains but 

 one flower. This can happen only in two cases : first, 

 when a simple stem is terminated by a single flower, and 

 all further growth is consequently arrested, as in the 

 Dog-tooth Violet ; and secondly, when but a single 

 flower is developed from each node, as in the Chick-Pea, 

 a native of Southern Europe. 



334. In respect to the order of the evolution, In- 

 florescence is of two principal kinds the CENTRIFUGAL, in 

 which the terminal flower is first unfolded, and the blos- 

 soming proceeds outward, as in the Elder and Pink 

 tribes ; and the CENTRIPETAL, when the outermost, or 

 lowest flower is first open, and the evolution proceeds 

 toward the centre, as in the Fennel and Cress tribes. 

 The first of these is called DETERMINATE INFLORESCENCE, 

 because the central flower stands in the place of the ter- 

 minal bud, and always terminates the axis of growth, as 

 in fig. 1 ; and the second is called INDETERMINATE IN- 

 FLORESCENCE, because it is entirely axillary, or each 

 flower proceeds from an axil between the leaf and the 

 stem, and the primary axis is never terminated by a 

 flower, as in fig. 2. Sometimes both these modes are 

 combined in the same plant, as in the Aster, Burdock, 

 and the great Order Composites generally, and also in 

 the Mint tribe, to which the Lavender, Sage and Penny- 

 royal, belong. In the first, the inflorescence of the single 

 head is developed centripetally, while that of the whole 

 cluster proceeds centrifugally ; that is, the outermost 

 flowers in the head expand first, and the blossoming pro- 

 ceeds inward, while the highest heads are first unfolded, 



What component part its name when not present what leaves docs It 

 bear axis of a compound peduncle Its divisions ? Define Scape Solitary 

 n florescence. Two principal forms of Inflorescence. Define the Centripetal 

 Centrifugal which is termed Definite which Indefinite? Why? How is 

 the primary axis in the Centrifugal mode the Centripetal ? Order of evoln' 



and the general evolution proceeds outward. In the 

 Mint family, this order is exactly reversed ; the inmost 

 flowers, and outermost or lowest clusters, always taking 

 the lead. 



CENTRIPETAL INFLORESCENCE. 



335. The principal varieties of this mode are the 

 Spike, Raceme, Corymb, Panicle, Ament, Spadix, Um- 

 bel, Head, and Thyrse. 



336. THE SPIKE is formed by the production of 

 numerous sessile flowers on an elongated rachis, as in the 

 Plantain, and the Darnell grass, fig. 9. 



337. THE RACEME is a spike with the flowers arranged 

 on pedicels, as in the Currant, fig. 6. 



338. THE CORYMB has the same general law of 

 arrangement as the raceme, but the lower pedicels are 

 elongated, so to form a flat or flattish top, as in the Yar- 

 row, fig. 3. 



339. THE PANICLE is a loose, irregular cluster, com- 

 bining the characters of a corymb and raceme, and is, in 

 fact, a kind of branching spike. The Oat, fig. 4, is a 

 familiar and beautiful example. 



340. A THYRSE is a more compact arrangement of 

 the panicle, and generally has a somewhat ovate form, as 

 in the Grape and the Lilac, fig. 8. 



341. When the inflorescence is compound, two or 

 more of these forms are combined ; and they are expressed 

 by a similar combination of terms, as, panicles thyrsoid 

 Racemes corymbose Spikes panicled, and the like. 

 The species of Grass at fig. 7 has a compound inflorescence 

 of the latter form. 



342. AN AMENT, or CATKIN, is a spike with sessile 

 bracts interposed among its flowers, as in the Walnut 

 and Willow, figs. 2 and 7, Plate XXI. A large number 

 of our forest trees have this form of inflorescence. 



343. THE SPADIX is a spike with a greatly thickened, 

 club-shaped rachis, surrounded by a single bract, called 

 a spathe, as in the Calla and Palm tribes. At fig. 9 is 

 seen the spadix, with its two kinds of flowers, the fertile 

 ones being included in the lower whorls; and at fig. 10 

 the spadix is inclosed by its spathe, as in the American 

 Calla. 



344. THE UMBEL is formed when all the stalks radi- 

 ate from a common centre, like the rays of a star. It is 

 simple, when each of the pedicels bears a single flower, 

 as in the Milk-weed ; and compound, when each of the 

 flower stalks bears a smaller umbel, as in the Dill, fig. 5, 



tion in the Composite In the Mint tribe. Forms of Centripetal Inflorescence. 

 Define each, with examples. Centrifugal forms Define. Examples. Differ- 

 ence between the Thyrse and Panicle, the Raceme and Spike, Fascicle and 

 Corymb, Cyme and Umbel. 



