The main axis generally terminates in a flower, and the lateral axes branch in a cymose manner (Fig. [371]). The flowers show the following differences in construction: VERTICILLATE (EUCYCLIC), i.e. constructed all through of alternating whorls: Aquilegia (Fig. [370]), Xanthorhiza, and sometimes Eranthis. Semiverticillate (HEMICYCLIC) i.e. with sepals and petals in alternate whorls, and the others arranged spirally: Ranunculus (Fig. [371]), Myosurus, Pæonia and several other genera entirely, or in certain species only. Spiral-flowered (ACYCLIC) i.e. all the leaves are arranged spirally, so that sepals and petals do not alternate the one with the other, even though they are the same in number: Adonis (Fig. [372]), Aconitum, Delphinium-species, Nigella-species, Helleborus. The leaves of the calyx are in this instance arranged on a spiral of 2/5; those of the corolla on 2/5, 3/8, 5/13 or 8/21, and stamens and carpels likewise on higher fractions of the same series.
The genera Caltha, Anemone, Thalictrum and Clematis have a single perianth, which is most frequently petaloid; it is thus apparent that the sepals are petaloid, and the leaves, which in other genera have developed as petals, are in these instances stamens. The calyx is similarly petaloid in the genera Helleborus, Eranthis, Nigella, Delphinium and Aconitum; but the petals are present in these instances in unusual (horn-like) forms, and almost entirely given up to the function of nectaries, a function they already possess in Ranunculus. According to a more recent theory the “honey-leaves” are transformed stamens, which have lost the function of reproduction; the perianth is then single, and most frequently petaloid. [Those leaves in the flowers of many Ranunculaceæ which bear nectaries are termed by Prantl honey-leaves, and comprise those leaf-structures of the flower whose essential function lies in the production of nectar, and which, independent of the differentiation of the perianth into calyx and corolla, are derived from the stamens by the loss of their reproductive functions. Clear transitional forms are found between the two series of the perianth (e.g. between the sepaloid and petaloid perianth-leaves of Anemone japonica, A. decapetala, Trollius-species) while transitional forms are never found between perianth-and honey-leaves (with the exception of Aquilegia vulgaris, var. stellata). In Anemone and Clematis the honey-leaves pass gradually into the stamens, and agree with the stamens in the other Ranunculaceæ in their arrangement, development, and scant system of veins (except Nigella). In Delphinium, sect. Consolida, the two honey-leaves placed in front of the unpaired perianth-leaf are united into one, as shown by the veins (twice three veins arranged symmetrically). The honey-leaves of Aquilegia, Callianthemum, and the majority of the Ranunculus-species serve by reason of their large circumference, as organs of attraction, and on this account are considered as petals by other authors.—The same position in the flower which the honey-leaves assume is found occupied by staminodes, without nectar, in some Coptis-species, in Anemonopsis, Actæa sect. Euactæa, (e.g. A. racemosa), Clematis sect. Atragene; in the last-named they closely surround the stamens, in Actæa they are petaloid.—A perianth, sharply differentiated into calyx and corolla, and destitute of honey-leaves, is found in Anemone, sect. Knowltonia (Cape),
Adonis, Pæonia.—The perianth of the Ranunculaceæ is considered by Prantl to be usually petaloid.—The nectaries arise in the Ranunculaceæ (1) on normal stamens (Clematis sect. Viorna), (2) on the honey-leaves (this is generally the case), and (3) on the carpels (Caltha and the majority of Trollius-species).—As the result of his researches upon the Ranunculaceæ, Prantl does not agree with the view advanced by Drude (Schenk, Hand. d. Bot. iii.) that the petals in general have proceeded from the metamorphosis of the stamens (K)].
Fig. 373.—Ovaries in longitudinal section: v the ventral suture; d the dorsal suture: A, B Clematis; C Ranunculus; D Myosurus.
The most primitive form of fruit is undoubtedly the pod formed by one carpel, on the edges of which (along the ventral suture) two rows of ovules are situated: Pæonieæ, Helleboreæ, Delphinieæ (Fig. [379]). In a great many genera the number of ovules has been limited to one perfect one, which is placed in the central plane under the united leaf-edges, and sometimes also some barren ovules above it (Fig. [373]). The fruitlets in this case become achenes, and are present in much larger numbers than when there are follicles.
Fig. 374.—Helleborus niger: A flower; B receptacle; pet petals (honey-leaves); pi stamens and carpels; C seed; D anther (cross section); alb endosperm.
Fig. 375.—Caltha palustris: fruit.