Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/134

124 BOTANY [REPRODUCTIVE ORGANS. into the state of f rait. At its base two leaves are produced, each of which is capable of developing buds. These are flower-buds, and constitute secondary axes a" a", ending in single flowers/"/ , which are thus terminal and solitary; and at the base of these axes a pair of opposite leaves is F ig. 164. Gentianella (Gentiana acautis). a, axis ; 6, flower ; c, bract. Fig. 165. Flowering branch of Erythrcca Centaurium. produced, giving rise to tertiary axes a " a " a ", ending in single flowers/ " / " f", and so on. The term dichotomous has also been applied to this form of cyme. But these terms are not strictly correct, for here there is no dichotomous branching, although, when the terminal flower / of the generating axis has withered, an apparent dichotomy occurs ; but the lateral axes on the several shoots are produced monopodially, and therefore the term is apt to lead to con fusion regarding the development of the shoots. The name dichasium has, therefore, been substituted for the old term. In the natural order Caryophyllacese (Pink family) the dichasial cymose form of inflorescence is very general. In some members of the tribe, as Dianthus barbatus, D. Carthusianorum, &c., in which the peduncles are short, and the flowers closely approximated, with a centrifugal expansion, the inflorescence has the form of a contracted dichasium, and receives the n&ro.Q of fascicle (fig. 1G6). A Fig. 166. Fascicle of Mallcw (ifalva sylvcstris). similar inflorescence is seen in Xylophylla longifolia. When the axes become very much shortened, the arrangement is more complicated in appearance, and the nature of the in florescence can only be recognized by the order of opening of the flowers. In Labiate plants, as the Dead-nettle (Lamium), the flowers are produced in the axil of each of the foliage leaves of the plant, and they appear as if arranged in a simple whorl of flowers. But on examination it is found that there is a central flower expanding first, and from its axis two secondary axes spring bearing solitary flowers ; the expansion is thus centrifugal. The inflorescence is there fore a contracted dichasium, the flowers being sessile, or nearly so, and the clusters are called verticillasters (fig. 1G7). Fig. 167. Flowering stalk of the White] Dead-nettle, (Lamium album). The bracts 6. 6 are like the ordinary leaves of the plant, and produce clusters of flowers in their axil. The clusters are called verticillasters, and consist of flowers which are produced in a centrifugal manner. Sometimes, especially towards the summit of a dichasium, owing to the exhaustion of the growing power of the plant, only one of the bracts gives origin to a new axis, the other remaining empty ; thus the inflorescence becomes unilateral, and further development is arrested. In addition to the dichasial form there are others where more than two lateral axes are produced from the primary floral axis, each of which in turn produces numerous axes. To this form the terms trichotomous and polytomous cyme have been applied ; but these are now usually designated cymose vimlels. They are well seen in some species of Euphorbia. Another term, anthela, has been used to distinguish such forms as occur in several species of Luzula and Juncus, where numerous lateral axes arising from the primary axis grow very strongly, and develop in an irregular manner. In the uniparous cyme a number of floral axes are successively developed one from the other, but the axis of each successive generation, instead of producing a pair of bracts, produces only a single one. The basal portion of the consecutive axes may become much thickened and arranged more or less in a straight line, and thus collectively form an apparent or false axis or sympodium, and the inflorescence thus simulates a raceme. In the true raceme, however, we find only a single axis, producing in succession a series of bracts, from which the floral peduncles arise as lateral shoots, and thus each flower is on the same side of the floral axis as the bract in the axil of which it is de veloped ; but in the uniparous cyme the flower of each of these axes, the basal portions of which unite to form the false axis, is situated on the opposite side of the axis to the bract from which it apparently arises (fig. 1G8). This bract is not, however, the one from which the axis termin ating in the flower arises, but is a bract produced upon it, and gives origin in its axil to a new axis, the basal por tion of which, constituting the next part of the false axis, occupies the angle between this bract and its parent axis, the bract from which the axis really does arise being situated lower down upon the same side of the axis with itself. The uniparous cyme presents two forms, the scor- pioid or cicinal and the lielicoid or bostrychoid. In the scorpioid cyme the flowers are arranged alter nately in a double row along one side of the false axis (fig.

1G9) the bracts when developed forming a second double