of such markings, as seen in the genus Erodium, is shown in [Fig. 14]. It is interesting to note the various ways in which flowers render themselves conspicuous in order to attract insects. In the majority of Seed Plants, such as the Buttercup, Pea, Rose, Foxglove, it is the corolla, formed either of separate petals, as in the first three, or of petals fused together, as in the last, which by its bright colour or colours renders the flower noticeable. In other species the calyx takes on the function of advertisement, the corolla being in comparison insignificant—we may study examples of this in the Anemones, Hellebores, and Marsh Marigold (Caltha palustris). It is worth examining this last, to see how its coloured sepals resemble and fulfil the same function as the petals of its cousins the Buttercups. Or, again, sepals and petals may combine in showiness, both sets being brightly coloured in one or more tints—compare the Columbine (Aquilegia), Larkspur (Delphinium), Milkwort (Polygala), and the marvellous flowers of Orchids. In the great group of the Monocotyledons, indeed, to which
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.
Fig. 16.—Dwarf Cornel (Cornus suecica), 2/3, and single flower enlarged.
In a large number of flowers such general feasting is discountenanced, insect traffic is regulated, the visits of insects of little or no service to the plants is discouraged, and special arrangements are made to attract and minister to the needs of those insects whose visits are of most benefit. Except where flowers are borne in clusters, creeping creatures like ants are of no service; for in the course of the journey “by land” from one flower to another, there is a strong probability of any pollen which the insect may be carrying being rubbed off before the next blossom is reached; small flying insects are likewise frequently useless. In many plants the visits of such pedestrians and small fry is very distinctly discouraged. Of different devices which serve this end, the most conspicuous and effective include barriers to the passage of stem-climbers, and devices in the flower preventive of the visits of unwelcome guests. We may take a few instances from among British plants, which the reader may with a little diligence find and study for himself. Several members of the Pink family (Caryophyllaceæ) produce a sticky secretion which is a very effectual bar to the passage of small walking animals. In the English Catchfly (Silene anglica), Night-flowering Catchfly (S. noctiflora) and the Nottingham Catchfly (S. nutans), hairs are present all over the leaves and stems, from the tips of which a gummy substance exudes, which is a fatal trap for small insects. Kerner, in his interesting book, “Flowers and their Unbidden Guests,” states that on the sticky stems of the last, in the Tyrol, he identified the remains of sixty different kinds of insects—ants, ichneumons, beetles, bugs, flies, and so on. The Red German Campion (Lychnis Viscaria) has an extremely sticky ring below each joint of the stem and inflorescence, which is most fatal to any creature which attempts to climb to the flowers. Other instances, such as the Petunia or Moss Rose, will occur to the reader. Another familiar kind of barrier is the presence on the calyx or involucre of a palisade of stiff hairs or prickles, such as may be studied in the Thistles; in some plants a downward-pointing ring of stiff hairs at each joint serves the same purpose. In the Japanese Wineberry (Rubus phœnicolasius), often grown in gardens, the calyx, like the stem, is densely clothed with bright red slender spines ([Fig. 17]). It opens to allow the inconspicuous petals to expand, and then closes again and resumes its protective rôle till the scarlet fruit approaches maturity.