Dicentra (syn. Dielytra) and Adlumia have a doubly symmetrical flower, with a spur or gibbous swelling at the base of each of the laterally-placed petals (Figs. [393] A, [394]). Corydalis has a zygomorphic flower, only one of the lateral petals having a spur, and consequently there is only one nectary at the base of the bundle of stamens, which stands right in front of the spur (Fig. [393] B, [395], [396]). The fruit is a many-seeded siliqua-like capsule. A peculiarity of the flower is that the plane of symmetry passes transversely through the flowers, whilst in nearly all other zygomorphic flowers it lies in the median line. Moreover, the flower is turned, so that the plane of symmetry ultimately becomes nearly vertical, and the spur is directed backwards.—Many species have subterranean tubers; in these the embryo germinates with one cotyledon, which is lanceolate and resembles a foliage-leaf. The tuber is in some the swollen hypocotyl (C. cava), in others a swollen root (C. fabacea, etc.), which grows down through the precisely similar swollen root of the mother-plant. The sub-genus Ceratocapnos has dimorphic fruits (nuts and capsules) in the same raceme. Fumaria differs from Corydalis only by its almost drupaceous, one-seeded nut (Fig. [395]).
Fig. 393.—Diagram of Dicentra (A), Corydalis (B), and Hypecoum (C).]
Fig. 394.—Dicentra spectabilis: A flower (2/5); B the same, after removal of half of one outer petal; the cap, formed by the inner petals, is moved away from the anthers and stigma; the insect does this with the lower side of its abdomen, and thus rubs the stigma on the hairs of its ventral surface; the dotted line at e indicates the direction of the proboscis; C andrœcium and gynœceum; D stigma.
The structure of the flower. Hypecoum among the Papaveraceæ is the connecting link with the Fumariaceæ. The diagram (Fig. [393] C) corresponds both in number and in the relative position of its members with that of most of the other Papaveraceæ (Fig. [391]), except that there are only four stamens (with extrorse anthers). In Dicentra (Fig. [393] A), the two central (uppermost) stamens are absent, but each of the two lateral ones are divided into three filaments, of which the central one bears a four-locular anther, and each of the others a two-locular (half) anther. Corydalis and Fumaria stand alone in the symmetry of the flower, differing from Dicentra in having only one of the lateral petals (Fig. [393] B, sp) prolonged into a spur, while in Dicentra both the petals are spurred. This structure has been interpreted in various ways. According to Asa Gray the median stamens are absent in the last-named genera, and the lateral ones are split in a similar manner to the petals of Hypecoum. Another, and no doubt the most reasonable theory (adduced by De Candolle), is: that two median stamens are split, the two parts move laterally, each to their respective sides and become united with the two lateral stamens; this affords a natural explanation of the two half-anthers, and establishes a close relationship to the Cruciferæ. A third interpretation, held by Eichler and others, is as follows: the median stamens are always wanting; when they appear to be present, as in Hypecoum, it is due to the fact that the side portions of the lateral stamens approach each other (as interpetiolar stipules) and coalesce into an apparently single stamen.
Fig. 395.—Fumaria officinalis: A the flower in longitudinal section; B the andrœcium and gynœceum; nectary to the right.
Fig. 396.—Corydalis cava: a a flower (lateral view); b the anthers lying round the stigma; c the anthers shortly before the opening of the flower; d the head of the stigma; e relative position of the parts of the flower during the visit of an insect.