Convolvulaceae

The well-known Convolvulus and the singular little Dodder (Cuscuta) are the only British genera belonging to this family.

Cuscuta is a leafless, annual, parasitic plant, with thread-like sterns. The flowers are small, nearly globular, and grow in lateral heads or clusters. One species attacks the clover, and is sometimes sufficiently abundant to do much mischief.

We have in England three species of Convolvulus - C. arvensis, C. sepium, and C. soldanella.

C. arvensis being melliferous and slightly sweet-scented, is much visited by insects. The honey is situated below the bases of the stamens, which are somewhat flattened and bent inwards, so that the insect can only reach the honey by pressing its proboscis down between them. The stigmas and anthers mature at the same time; but as the former project above the latter, they are necessarily touched first. If the visits of insects be too long deferred, the flower fertilises itself. C. arvensis closes in wet weather and at night.

C. sepium, on the contrary, remains open during rain, but closes at night, unless there be a moon, when it remains expanded. It has no smell, and is perhaps, on that account, in spite of its large size, comparatively little visited by insects.

Solanaceae

The British genera are the following: Hyoscyamus (the Henbane), Solanum (the Nightshade), and Atropa. Datura is sometimes found growing wild, but it is not a true native.

Solanum secretes no honey, and is little visited by insects. Hyoscyamus, on the contraiy, is melliferous, and cross-fertilisation is favoured by the projection of the stigma beyond the anthers.

Orobanchaceae

A curious family, with simple or rarely-branched stems, and scales instead of leaves. The species are either brown or purplish, but never green, and are parasitical on the roots of other plants. There are two British genera: Orobanche (Broomrape) and Lathroea; both are parasitic. In Lathraea the scale-like leaves are hollowed out, the inner surfaces being provided with peculiar structures of two kinds; both consist of three cells, two of which are spherical, and situated on the third, which in the one sort is cylindrical, so that they resemble glandular hairs; m the second sort the basil cell is flattened. These organs have been described as possessing the power of throwing out protoplasmic extensions, but this has not yet been confirmed.