CXXXVII.— THE BROOM. 
Sarothamnus scoparius Wimmer. 
T he large pea-like blossoms of the Broom, “ yellow and bright as bullion 
unalloyed,” swinging freely in the wind on slender foot-stalks from the glossy 
green flexible shoots have quite an exhilarating effect on the beholder. Like many 
other Leguminosce, the shrub seems to luxuriate in a warm dry soil, especially pure 
sand, and in the sunniest aspect, as if reminiscent of an origin Mediterranean rather 
than northern, recking little of a scarcity of water or of exposure to wind. Though 
absent from the mainland of Scandinavia, it is distributed over the whole of Britain 
and ascends to altitudes of 2,000 feet in the Scottish Highlands. Its tough 
woody stems may in time reach five or six feet in height and are surmounted by a 
dense mass of long, erect, flexible, and angular twigs. These are tough, furrowed, 
and of a bright green, becoming bluer with age, and are clothed with fine silky hairs. 
Their stomata, or transpiration-pores, are confined to the bottoms of the furrows; so 
that, although small leaves do exist, the plant is obviously adapted to the economy 
of water by a lessened transpiration which its habitat suggests. 
The little leaves are stalked and mostly ternate, the obovate leaflets being from 
a quarter to half an inch long ; but the upper ones have generally only a single 
leaflet. The stipules are minute and the leaves, when young, are silky. Leaves are 
sometimes almost absent and, in any case, the green branches perform most of their 
physiological functions in the plant’s economy. 
The gay blossoms form one of the glories of the month of May ; and, though 
they yield no honey, are visited by many bees and other insects for the sake of their 
pollen. These visits would seem to be wellnigh essential to pollination. Darwin 
writes : — - 
“ In tlie Broom, if the flowers be protected from insects, the parts [stamens and pistils] do not spring out, and scarcely any 
polls are produced." 
The pollination-mechanism belongs to the explosive type and is similar to that 
of Genista and Ulex, with some differences in detail. Of the ten stamens, five are 
long and five are short ; and pollen is thus shed so as to accumulate near the tip of 
the keel (the two petals forming this being united along both edges) and also about 
half-way along its length. The long spirally-coiled style is very characteristic. It 
brings the stigma, which is later than the anthers in maturing, into the extreme tip 
of the closed keel. When a bee alights on an opening flower-bud, the pressure of 
its hind feet separate the wing petals, and the keel begins to split along its upper 
edge from its base towards its apex, probably from an irritability of the claws of its 
petals when touched by the insect’s proboscis, as is the case in Genista. The shorter 
stamens then alone emerge and dust the under side of the bee’s body with pollen. 
If greater pressure be produced, as by the weight of a heavy humble-bee, or when 
the flower is a day or two older and is visited for a second time, the split extends 
