The flower has 5 sepals (the median, as usual, posterior), 5 petals, 5 stamens and 2 carpels (in the median line) (Fig. [528]). The calyx is often scarcely indicated. The petals have a short claw are most frequently obcordate, or have an incurved apex (Fig. [528] B, C), being incurved in the bud; they are white, rarely yellow (Fennel and Parsnips), blue or red. The flowers are sometimes zygomorphic, especially those on the circumference of the umbel, and in that case it is the petal which is directed outside (anterior) which is the largest, and the two posterior are the smallest (e.g. Heracleum). The stamens are incurved in the bud. The 2 free styles unite at the base into the “stylar-foot” (stylopod), a swollen nectary (Fig. [528] B, C); the ovary is bilocular, the raphe of the ovules being directed inwards. The fruit is a schizocarp, dividing into two mericarps; the plane in which these separate coincides with that of the union of the carpels, and the two nut-like mericarps are in most genera kept together for awhile at the top of a thin, bifid, or undivided stalk (carpophore) which is in direct continuation with the flower-stalk (Fig. [537]). Each mericarp has most frequently 5 more or less strongly projecting ridges, the primary ridges (Figs. [530], [532], [534], [535], etc.), of which 3 lie on the back of the mericarp, the dorsal ridges, and 2 on its edge near the plane of division, the marginal ridges; five of these (10 ridges in all in the entire fruit) are placed opposite the calyx-teeth and the others between them. In some genera there are in addition 4 secondary ridges to each mericarp between the primary ones (Fig. [528] E: the secondary ridges bear the long bristles). Inside these secondary ridges, or inside the grooves between the primary ridges, when the secondary ridges are absent, oil ducts (vittæ, schizogenous ducts) are found in the pericarp, most frequently one in each groove; two are also often found on the ventral side of each mericarp (Figs. [528] E, 530 ol, etc.). The seed is most frequently united with the pericarp. The embryo is small and lies high up in the large, most frequently horny endosperm (Fig. [528] D).—The endosperm does not contain starch, but oil, and presents three different forms, of important systematic value: (a) those which are quite flat on the ventral side (i.e. the side turned towards the plane of splitting) (Figs. [528] E, [530], [531], [534], etc.): the majority of the genera, Orthospermeæ (e.g. Carum, Pastinaca); (b) those in which the endosperm on the ventral side is provided with a longitudinal groove, often deep: Campylospermeæ (e.g. Anthriscus); the transverse section is nearly a crescent (Fig. [532]); (c) those in which the endosperm is concave on the ventral side (hollow in both longitudinal and transverse sections): Cœlospermeæ (e.g. Coriandrum) (Fig. [538]).
The genera are distinguished first of all by the endosperm and forms of fruit, the ridges and oil-ducts; then by the form of the umbel, the calyx and corolla, by the absence or presence of an involucre, etc.
Fig. 529.—Hydrocotyle vulgaris. Transverse section of fruit.
1. Hydrocotyleæ, Penny-wort Group. Capitula or simple umbels (all the other groups have compound umbels). No oil-ducts. Orthospermous.—Hydrocotyle (Penny-wort). The fruit is considerably compressed laterally (Fig. [529]). The calyx-teeth are small. The leaves are peltate.—Didiscus.—Sanicula (Sannicle). The umbels are small, capitate, generally collected in a raceme; calyx-teeth distinct. ♂-and ♀-flowers in the same umbel. The fruits are round, studded with hooked bristles. No carpophore.—Astrantia has an umbel surrounded by a large, often coloured involucre, with this exception it is the same as the preceding, but the fruit is slightly compressed, with 5 equal ridges. Hacquetia (Dondia).—Eryngium (Sea Holly): leaves often thorny. The flowers are all sessile, the inflorescence is thus a capitulum; each flower is often subtended by a bract, which is thorny like the involucre, resembling the burrs of the Teasel. The sepals are large.—Lagœcia: one of the loculi of the ovary is suppressed.
Fig. 530.—Fruit of Carum petroselinum: fr endosperm; ol oil-ducts.
Fig. 531.—Pimpinella. Transverse section of fruit.
2. Ammieæ, Caraway Group (Figs. [530–532]). The fruit has only the 10 primary ridges; it is usually short, almost spherical or broadly ovate and distinctly compressed laterally. Oil-canals are most frequently present. Orthospermous (except Conium).—Cicuta (Cow-bane). Pointed calyx-teeth. Glabrous herbs with pinnate or bipinnate leaves. C. virosa has a thick, vertical rhizome, divided by transverse septa into many compartments; the leaflets are narrow, lanceolate, and dentate; the large involucre is wanting.—Apium (Celery). No calyx-teeth. A. graveolens, a maritime plant, has neither large nor small involucre; the umbels are short-stalked or sessile.—Carum (Caraway). Calyx-teeth small; the large involucre is wanting or is only few-leaved. C. carvi (Caraway). C. petroselinum, (Parsley) (Fig. [530]). Falcaria; Ammi; Helosciadium; Bupleurum (Hare’s-ear) with simple leaves and yellow corolla; Pimpinella (Fig. [531]); Sium; Ægopodium (A. podagraria, Gout-weed) has bi- or tri-ternate leaves, with ovate, dentate leaflets; the large involucre is wanting.—Conium is campylospermous (Fig. [532]); the short, broadly ovate fruit has distinctly projecting, often wavy crenulate ridges. C. maculatum (Hemlock) has a round, smooth stem with purplish spots.