[Illustration: FIG. 15.--UMBEL OF ASTRANTIA CARNIOLICA, SHOWING PETAL-LIKE RING OF COLOURED LEAVES (BRACTS). 1/1.] the Orchids belong, sepals and petals usually combine in form and colour to form one corolla-like envelope (then called a _perianth_). In many other plant groups--for instance, the _Dipsacaceæ_ (such as the Scabious), _Umbelliferæ_, and _Compositæ_--conspicuousness is obtained by a grouping together of a large number of small flowers. In the Cow Parsnep (_Heracleum Sphondylium_) the outer petal of the marginal flowers of the large umbel is much enlarged, which enhances this effect. In _Astrantia_, an interesting genus of _Umbelliferæ_, the bracts take on the appearance of a ring of large petals, and surround the group of small flowers (Fig. 15). The same thing may be noticed in the outer blossoms of the close flower-head of the Field Scabious (_Knautia arvensis_). In many _Compositæ_ the process is carried still farther; in the Common Daisy (_Bellis perennis_) the outer flowers have each a long strap-shaped expansion of the corolla, which is of a different colour (white) from that of the corollas of the inner flowers, which are yellow. In the Dandelion (_Taraxacum officinale_) all the flowers have a yellow strap-shaped corolla. In the Guelder Rose (_Viburnum Opulus_) the outer flowers are entirely devoted to advertisement, consisting each of a big white corolla, while only the small inner flowers possess stamens and pistil and are capable of producing the brilliant scarlet berries. In a cultivated form of this, commonly called the Snowball Tree, the advertisement flowers only are present, forming a globe of white blossom, and no fruit is produced in consequence. The Dwarf Cornel (_Cornus suecica_), a little Dogwood growing on many Scottish moors, bears what looks like a white flower with a purple centre. On examination it is seen that the four white petal-like structures are really foliage-leaves, which have taken on the duty of advertising the group of small purple blossoms which they enclose (Fig. 16). A similar and very gorgeous effect is produced in several Spurges often seen in greenhouses, such as _Euphorbia fulgens_, _E. splendens_, and _E. punicea_; in these the upper foliage-leaves are large and coloured brilliant scarlet, the flowers which accompany them being quite small. These aggregations of flowers with their flaunting flags are in general an invitation to all comers; the nectar in the blossoms lies open to every hungry insect, and pollination is effected in a rather promiscuous and messy way; not only flying insects--bees, butterflies, beetles, and flies of many sorts--but also ants and other creatures which creep up the stems from the ground, assemble for the feast, and incidentally transfer from flower to flower pollen which may adhere to their bodies. [Illustration: FIG. 16.--DWARF CORNEL (CORNUS SUECICA), 2/3, AND SINGLE FLOWER ENLARGED.]