Fig. 433.—Transverse and longitudinal section of seed: bl the cotyledons; k the plumule; R the radicle; fr the endosperm; sk the testa.
Linum (Flax) has 5-merous flowers. The main axis terminates in a flower; and the succeeding branching is cymose, or unipared scorpioid branching by unilateral development, and the flowers in consequence of the vigorous sympodial development of the lateral axis (and also by the leaves being displaced and pushed aside), assume a position apparently lateral (i.e. racemose) without bracts; each branch of the sympodium generally has 2 leaves. The testa is shining and smooth when dry, but its external cellular layer becomes mucilaginous in water.—Radiola has a 4-merous flower. It is a small herb with opposite leaves, and regular, dichasial branching.
The anthers and stigmas in L. catharticum and usitatissimum develop simultaneously, and cross-pollination as well as self-pollination takes place. L. grandiflorum, perenne, and others, are dimorphic (short-and long-styled). There are 5 nectaries outside the stamens.
130 species; Linum and Radiola are native genera.—L. usitatissimum is extensively cultivated in Europe (especially in Russia and Belgium), N. America and elsewhere (its home no doubt being Asia), partly on account of the oil (linseed oil) which is extracted from the seeds, and partly on account of the bast of the stem, which has very thick-walled cells. The seeds and oil are OFFICINAL. The species cultivated in ancient times was L. angustifolium. Several species are cultivated as ornamental plants.
Order 3. Geraniaceæ. The majority are herbs with dichasial branching, and scattered or opposite, stalked, palminerved (rarely penninerved) leaves with small stipules. The flowers are regular (except Pelargonium) and 5-merous, with 10 or 5 stamens, which are slightly united at the base. Nectaries alternate with the corolla-stamens. The ovary is most frequently 5-locular, deeply 5-grooved, and bears 1 well developed style (“beak”), which towards the apex divides into 5 branches bearing stigmas; ovules 1 in each loculus, pendulous or ascending. The 5 carpels become detached from one another when ripe, and bend or roll back (Fig. [434]) or become spirally twisted in the upper “beak-like” part (Figs. [435], [436]), whilst a central column (septal column) persists; each carpel, in consequence, remains either closed, and the fruit is a 5-merous schizocarp whose nut-like lower portion, containing the seed, is forced into the ground, thus burying the seed by the movements of the spirally-twisted, hygroscopic “beak” (Figs. [435], [436]); or it opens along the ventral suture, so that the seeds may fall out, and it is then a 5-valved capsule, with septicidal dehiscence (Fig. [434]) and the rolling up often takes place so suddenly and violently that the seeds are shot out to considerable distances. The embryo is usually green and curved, and the cotyledons are folded; endosperm is wanting.
Geranium (Crane’s-bill) has 5 + 5 stamens,and a septicidal capsule; the carpels most frequently remain suspended from the apex of the column (Fig. [434]). The leaves are most frequently palminerved. The flowers are situated solitarily or 2 together (2-flowered scorpioid cyme).—Erodium (Stork’s-bill); inflorescence a many-flowered unipared scorpioid cyme, stamens 5 + 0 (petal-stamens are wanting), and fruit a schizocarp whose carpels become detached; their beaks are hairy on the internal surface and twist themselves spirally (Fig. [436]). The umbellate inflorescences are composed of multiflowered scorpioid cymes. The leaves are often penninerved.—The most primitive type is represented by Biebersteinia: S5, P5, A5 + 5, G5 (ovaries free, and styles united above); fruit 5 small nuts. The most advanced type is Pelargonium, which has zygomorphic flowers, the posterior sepal being prolonged into a spur which becomes adnate to the peduncle; the petals are unequal in size; some of the petal-stamens are often wanting. (Erodium may be slightly zygomorphic).
Fig. 434.—Geranium sanguineum. Fruit (3/1).
Fig. 435.—Pelargonium.