THE PETTY WHIN— continued. 
but in some cases, as in the plants represented in this and the three following Plates, 
the union between the upper portions of the sepals is so unequal that the calyx 
appears two-lipped. The ten stamens, which are inserted in two whorls, are 
generally diadelphous, the nine anterior being united into a split tube by the lower 
half of their filaments, whilst the posterior stamen is free ; but in the genera Genista, 
Ulex, Sarothamnus, and Ononis, the Greenweeds, Gorses, Brooms, and Rest-harrows, all 
ten stamens are united {monadelphons). 
Most PapilionatcB secrete honey at the base of the staminal tube, in which it 
accumulates round the base of the ovary. It is thus concealed and requires the 
insect obtaining it to have a moderately long tongue. The PapilionatcB are, in 
fact, bee-flowers, i.e. they are mostly pollinated by that highly-organised group 
of insects ; and this, like other examples of the highly-specialised structure and 
physiology of the group, points to its geologically-speaking recent origin. A 
heavy insect visiting one of the blossoms alights on the wing petals, often 
grasping them with its legs. These wing petals are usually interlocked with the 
keel petals within by a remarkable series of protuberances and hollows in the one 
moulded over those in the other, so that the two pairs of petals are depressed 
together by the bee’s weight. The anthers and stigmas are thus exposed, and pollen 
is usually dusted on to some portion of the bee’s body which in visiting another 
flower will come in contact with the stigma. The stamens are usually somewhat 
protandrous ; but, except in a few cases, self-pollination may occur if cross-pollination 
has failed to do so. 
In addition to many elaborate modifications of this mechanism for pollination, 
many Leguminosce have admirable contrivances to secure the dispersal of their seeds. 
One of the most frequent of these is well seen in the genus Genista, in the short pods 
of which an outer layer of cells becomes densely woody, while the inner layers are 
less dense. As these layers part with almost the last moisture they contain, in warm 
sunny weather, the denser layers contract more than the less dense, with the result 
that the pod splits open with a jerk, thus throwing the seeds to some distance from 
the parent plant. 
The nineteen genera, including in all some eighty species, of British Leguminoscs 
belong to six different Tribes. Of these, the GenistecB are shrubby plants, with leaves 
of three leaflets, ternately arranged, or reduced to one leaflet, or absent altogether, a 
two-lipped calyx, and monadelphous stamens. Its British representatives belong to 
the three genera Genista, Ulex, and Sarothamnus. 
