Fig. 586.—Cephaëlis ipecacuanha. Portion of a branch: st stipules.
4. Spermacoceæ. Chiefly small shrubs and herbs, many of which are weeds in tropical countries. The stipular sheaths bear numerous bristles at the edge. Spermacoce, Borreria, Diodia, Richardsonia, etc.
5. Stellatæ. Herbaceous plants with verticillate leaves (Figs. [587], [588–590]); the stipules are large, leaf-like, and resemble the lamina of the leaves, so that the leaves appear to be placed several in a whorl, while in reality there are only two opposite leaves, the stipules of which project freely, and are not erect (Fig. [587]).
Fig. 587.—Rubia tinctorum.
In some cases there are apparently 4 leaves in the whorl, and then 2 of these are leaves, and the other two are their interpetiolar stipules. When there are apparently 6 leaves, then the two of these which are opposite each other are leaves, and the other four are stipules; if there are several members in the whorl, then a division of the stipules has taken place. The proof of this theory is founded upon the fact that not more than 2 of the leaves of the whorl ever support buds (which, in addition, are seldom of equal vigour), and also that the whorls do not alternate with each other, which, according to the rules of the position of the leaves, they should do if all the members of a whorl had equal value. If there are, for instance, 4 members in two successive whorls, they stand right above one another, and do not alternate. The development and anatomical relations (the branching of the vascular bundles) also point to the same conclusion.—All the other groups of the order have only 2 small scale-like interpetiolar stipules, or they form at the base of the leaf-stalks an interpetiolar sheath, having often a toothed edge (Fig. [586]).—Another characteristic feature in this group is that the calyx is rudimentary, the corolla valvate (Fig. [588]), and that each of the two loculi of the ovary has only 1 ovule. The fruit is a schizocarp dividing into 2 fruitlets (Fig. [590]). The forms of the fruit, as well as many other characters, as, for example, the epigynous flower, the rudimentary calyx, the two free or almost free styles, present interesting analogous resemblances to the polypetalous order of the Umbelliferæ. This group has its home chiefly in the temperate regions of the northern hemisphere, especially about the Mediterranean; it is the only group which occurs in this country, represented by 4 genera.
Figs. 588–590.—Rubia tinctorum.
Fig. 588.—Diagram.
