Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/135

Rh FORMS OF INFLORESCENCE.] BOTANY 125 row on the opposite side, as seen in the Henbane ; the whole inflorescence usually curves on itself like a scorpion s tail, hence its name. In fig. 170 is shown a diagrammatic sketch of this arrangement. The false axis, abed, is formed by Fig. 170. Fig. 168. Fig. 169. Fia. 1C8. False raceme or helicoid cyme of a species of Alstrimieria. a a,&quot; a &quot; a&quot;&quot; lire separate axes successively developed, which appear to form a simple continu ous raceme, of which the axes fonn the internodcs. It is a definite uniparous inflorescence, however, with centrifugal evolution. Each of the axes is pro duced in the axil of a leaf, and is terminated by a flower/ /&quot;/ &quot; /&quot;, opposite to that leaf, and the axes have a spiral arrangement. FIG. 169. Scorpioidal or cicinal cyme of Forget-me-not (Myosotis paluslris). FIG. 170. Diagram of definite floral axes a, b, c, d, e. FIG. 171. Flowering stalk of a kind of Ragwort (Senecio). The flowers are in heads (capitula), and open from the circumference inwards in an indefinite centripetal manner. The heads of flowers, on the other hand, taken collec tively, expand centrifugally the central one a first. Each head of flowers terminates a separate axis. They form together a corymb of capitula. The inflorescence is called mixed. successive generations of unifloral axes, the flowers being arranged along one side alternately and in a double row ; had the bracts been developed they would have formed a similar double row on the opposite side of the false axis ; the whole inflorescence is represented as curved on itself. In fig. 169 the same scorpioid form of uniparous cyme is seen in the Forget-me-not, with the double row of flowers on one side of the false axis, but in this case the bracts, which should appear on the opposite side, are not developed, and hence the cyme is not complete. The inflorescences in the family Boraginacese are usually regarded as true scorpioid cymes. But it has been recently shown that in Myosotis (Forget-me-not) the axis is not a sympodium,but the branch ing takes place monopodially, therefore it should more cor rectly be regarded as a raceme with flowers only on one side and curving on itself. In Hyoscyamus (Henbane) and other Atropacece the branching is dichotomous, so that the inflorescence in this case also ought not to be regarded as a scorpioid cyme. In the helicoid cyme there is also a false axis formed by the basal portion of the separate axes, but the flowers are not placed in a double row, but in a single row, and form a spiral or helix round the false axis. In Alstrb meria, as represented in fig. 168 the axis a ends in a flower (cut off in the figure) and bears a leaf. From the axil of this leaf, that is, between it and the primary axis a arises a secondary axis a&quot;, ending in a flower/*, and producing a leaf about the middle. From the axil of this leaf a ter tiary floral axis a&quot;, ending in a flower / &quot;, takes origin. In this case the axes are not arranged in two rows along one side of the false axis, but are placed at regular inter vals, so as to form an elongated spiral round it. Compound definite inflorescences arc by no means com mon, but in Streptocarpus polyanthus, and in several Calceolarias, we probably have examples. Here there are scorpioid cymes of jxxirs of floivers, each pair consisting of an older and a younger flower. Forms of inflorescence occur, in which both the definite and indefinite types are represented ; these, then, are mixed Mixed in- inflorescences. Thus in Composite plants, such as Hawk- florescence, weeds (Hieracia) and Ragworts (Senecio, fig. 171), the heads of flowers, taken as a whole, are developed centri fugally, the terminal head first, while tiQ florets, or small flowers on the receptacle, open centripetally, those at the circumference first. So also in Labiatas, such as Dead- nettle (Lamium), the different whorls of inflorescence are developed centripetally, while the florets of the verti- cillaster are centrifugal. This mixed character presents dif ficulties in such cases as Labiatse, where the leaves, in place of retaining their ordinary form, become bracts, and thus might lead to the supposition of the whole series of flowers being one inflorescence. In such cases the cymes are described as spiked, racemose, or panicled, according to circumstances. In Saxifraga umbrosa (London-pride) and in the Horse-chestnut we meet with a raceme of scor pioid cymes ; in Sea-pink, a capitulum of contracted scorpioid cymes (often called a glomerulus) ; in Laurustinus, a compound umbel of dichasial cymes ; a scorpioid cyme of capitula in Vernonia centriflora. In the catkins of the Birch we have, in reality, spikes of contracted dichasial cymes. In the Bell-flower (Campanula), there is a racemose uniparous cyme. In the Privet (Ligustrum vulgare) there are numerous racemes of dichasia arranged in a racemose manner along an axis ; the whole inflorescence thus has an appearance not unlike a bunch of grapes, and has been called a thyrsus. TABULAR VIEW OF INFLORESCENCE. A. Indefinite Centripetal Inflorescence. I. Flowers solitary, axillary. Vinca, Veronica, hcdcrifolia, II. Flowers in groups, pedicellate. 1. Elongated form ( Raceme), Hyacinth, Laburnum, Currant. (Corymb), Ornithogalum. 2. Contracted or shortened form(Ulnbel), Cowslip, Astrantia. III. Flowers in groups, sessile. 1. Elongated form (Spike), Plantago. (Spikelet), Grasses. (Amentum, Catkin), Willov:, Hazel. (Spadix) Arum, some Palms. (Cone), Fir, Spruce. (Strobilus), Hop. 2. Contracted or shortened form (Capitulum), Daisy, Da. de- lion, Scabious. I V. Compound Indefinite Inflorescence. a. Compound Spike, Rye-grass. b. Compound Spadix, Palms. c. Compound Raceme, Astilbe. d. Compound Umbel, Hemlock and most Umlellifcrce. e. Raceme of Capitula, Pctasites. f. Kaceme of Umbels, Ivy. B. Definite Centrifugal Inflorescence. I. Flowers solitary, terminal. Gentianclla, Pccony. II. Flowers in Cymes. 1. Uniparous Cyme. a. Helicoid Cyme (axes forming a spiral,. I. Scorpioid Cyme (axes unilateral, two rows). Henbane.
 * Elongated form, Alstromeria.
 * * Contracted form, Witsenia corymbosa.
 * Elongated form, Forget-me-not, Symphytuni,
 * * Contracted form, Erodium, Alchemilla, arvenste*