TINY FLOWERS WHICH COMBINE TO ATTRACT

MANY plants produce small, or even diminutive, flowers which are nevertheless conspicuous because they are massed together in large numbers. The Hog-weed, or Cow-parsnip, is an example. Its individual flower consists of five minute sepals, alternating with which are five petals differing in size—especially in the outermost flowers of the group, or ‘umbel,’ where one petal of each is much larger than the other four. The pistil consists of two united carpels, while the five stamens shed their pollen before the stigmas are ripe. Each flower is furnished with a nectar-secreting disc, easily accessible to the short-tongued insects, such as flies and beetles, which are frequent visitors to the umbels of the Hogweed and its relatives.

The great Daisy family introduces us to another type of co-operative arrangement. Here, the inflorescence—called a ‘capitulum ‘—consists of very numerous small florets so closely associated that the appearance of a single bloom is produced. The common Daisy is a familiar example. Each of the tiny disc-florets is a perfect flower, with a tubular corolla which is often more than half filled with nectar. Also, the five anthers are united by their edges to form a tube, within which the pollen is shed, and from which it is gradually pushed out by the developing pistil, whose action resembles that of the piston of a syringe. Eventually, the stigma-lobes—rising clear of the pollen produced by their own flower—gape apart, thus exposing their receptive inner surfaces for pollination by insects coming from other blooms. But as the disc-florets open in succeeding ranks from outside inwards, cross-

pollination of two degrees is possible : viz. (1) between two florets of the same capitulum, and (2) between florets of distinct Daisies.

The outer—or ‘ray ‘—florets are very irregular in shape, the corolla consisting of a narrow tube below, which expands above into a white, pink-tipped strap. These florets have pistils, but no stamens. If pollen is brought to them, they can set seed; but probably their most important function is to render the capitulum as a whole conspicuous, and more attractive to insects, which seem to have a flair for symmetry and contrast.

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