Fig. 436.—Erodium cicutarium, detached carpel.
Pollination. The large-flowered Geranium-species are protandrous, e.g. G. pratense (one whorl of stamens opens first, and then the other, and succeeding these the stigmas, after shedding the pollen the stamens bend outwards); the small-flowered are also adapted, with various modifications, for self-pollination.—470 species; moderately hot climates, especially S. Africa.—Several Pelargonium-species, with numerous varieties, are ornamental plants (from S. Africa).
Order 4. Tropæolaceæ. Herbaceous, juicy plants which have scattered, long-stalked, peltate leaves without stipules, and often climb by their sensitive petioles. The flowers are situated singly in the axils of the foliage-leaves on long stalks, and are zygomorphic, the receptacle under the posterior sepal being prolonged into a spur; there are also differences between the posterior and anterior petals, the 2 posterior petals situated on the border of the spur being perigynous, and the edge of the anterior petals adjoining the claw fringed. After the 5 sepals (which are more or less coloured) and the 5 petals, follow 8 stamens (as the 2 median ones are suppressed, one from each whorl) and a gynœceum formed of 3 carpels; in each of the 3 loculi of the 3-grooved ovary is 1 ovule. The fruit is a schizocarp and divides into 3 1-seeded, drupe-like fruitlets, which do not (as in the Geraniaceæ) leave any pronounced column between them. Endosperm is wanting. The cotyledons are thick and sometimes slightly coalescent. Tubers often occur.
Fig. 437.—Diagram of Tropæolum: sp, spur.
Tropæolum.—About 40 species; all from America.
Pollination.—The spur is the receptacle for the nectar; the flowers are protandrous; the anthers open first, and one by one take up a position in front of the entrance to the spur, resuming their original position when the pollen is shed; the stigma finally takes their place after the filaments have bent backwards.—These plants have an acrid taste (hence the name “Nasturtium,” “Indian Cress”), on which account the flower-buds and young fruits of T. majus are used as capers. Some species are ornamental plants.
Order 5. Balsaminaceæ. Herbaceous, chiefly annual plants with juicy, brittle stems, so transparent that the vascular bundles may be distinctly seen. The leaves are simple, usually scattered, penninerved and dentate; stipules are wanting, but sometimes large glands are present in their place at the base of the petioles. The flowers are strongly zygomorphic; of their five 5-merous whorls the petal-stamens are suppressed (S5, P5, A5 + 0, G5); the sepals are coloured, the 2 anterior ones (Fig. [438] 3, 5) are very small or entirely suppressed, the posterior one is very large and elongated into a spur, and the 2 lateral ones pushed forward; sometimes the weight of the spur turns the flower completely round, so that the posterior leaves assume an anterior position; apparently only 3 petals, since the lateral and the posterior petals become united in pairs, and the anterior is larger and differently shaped; the 5 stamens have very short and thick filaments united at the base, and their anthers finally adhere together and remain in this condition, covering over the gynœceum; the filaments ultimately rupture at the base, and the entire anthers are raised on the apex of the gynœceum as it grows up. The gynœceum has a sessile stigma and a 5-locular ovary. The fruit is a capsule which, on maturity, opens suddenly when irritated, dividing into valves from the base upwards, and as the 5 valves roll up elastically, the seeds are shot out on all sides to considerable distances; a central column persists (Fig. [439]). The embryo is straight, and without endosperm.
