[Illustration: 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.