CLXXII.— THE COMMON ROCK-ROSE. 
Helianthemum C/mmcecistus Miller. 
L IKE the Tamaricacece and F rankeniacece , the Rock-rose Family, Cistacece, are an 
essentially xerophilous group. Unlike those two Families, but like many 
other Families in the Order Parietales, they have the relatively large and conspicuous 
but somewhat fugitive blossoms that specially mark the plants of sunny climes- 
The F amily comprises four genera, with some 160 species between them, of which 
120 belong to the genus Helianthemum, the only one represented in Britain. They 
are nearly all natives of the North Temperate Zone, especially of the Mediterranean 
region, growing in dry, sunny places with warm soils, sandy, or more frequently 
calcareous. Though sometimes annual and herbaceous, they are for the most part 
perennial shrubs or undershrubs with woody or wiry stems, and very often with 
evergreen, leathery, inrolled, heath-like leaves. It is in accordance with their usual 
places of growth that they have usually some glandular hairs on their surface, which 
may serve for the taking in of atmospheric nitrogenous gases. The presence or 
absence of stipules was correlated by the late Lord Avebury, as a means of 
protection for the buds, with the possession of narrow or of broad bases to the 
blades of the opposite simple and entire leaves. The flowers are perfect and 
polysymmetric and may be solitary or in unilateral cymes. They do not produce 
honey but, as in the Hypericacece, have an indefinite number of anthers, and thus 
produce an extra supply of pollen so as to attract insects. The calyx may be looked 
upon as having five distinct imbricate sepals, of which the two outermost are 
markedly different in size from the three inner ones, or the outer two may be 
considered as bracteoles. The petals, usually five in number, are convolute in the 
bud, overlapping one another in a different direction than do the inner sepals : 
they may be yellow, white, or various shades of orange, red, and pink, but are 
never blue : they have a remarkably delicate, tissue-paper-like texture ; and fade 
or fall off after being open for merely a day or two. The stamens are generally 
numerous and free, springing from a hypogynous disk : the three, five, or ten 
carpels are united into a superior one-chambered ovary, with more or less inrolled 
parietal placentas, unbent ovules, a single style, and three stigmatic lobes ; and the 
fruit is a capsule splitting into three or five valves along the midribs of the carpels. 
The seeds are albuminous with a curved embryo. 
The genus Helianthemum, originally so called by Valerius Cordus (1515-44) 
from the Greek 17X1,09, helios, the sun, avde^ov, anthemon, a flower, is specially 
characterised by its low growth, relatively smaller flowers than in Cistus, smaller 
outer sepals or bracteoles, more or less irritable stamens, and three-valved capsule. 
The first of these characters, in marked contrast to the shrubby species of the allied 
Cistus which are so striking a feature in the vegetation of the Mediterranean region, 
made the early botanists name it Chamcecistus, i.e. Dwarf Cistus, from the Greek 
