Fig. 202.—Stamens of Larkspur, surrounding the pistils.
In some cases (Fig. [203]) the stamens are longer than the pistil in one flower and shorter in another. If the insect visits such flowers, it gets pollen on its head from the long-stamen flower, and deposits this pollen on the stigma in the long-pistil flower. Such flowers are dimorphous (of two forms). If pollen from its own flower and from another flower both fall on the stigma, the probabilities are that the stigma will choose the foreign pollen.
Fig. 203.—Dimorphic Flowers of Primrose.
Many flowers are pollinated by the wind. They are said to be anemophilous (“wind loving”). Such flowers produce great quantities of pollen, for much of it is wasted. They usually have broad stigmas, which expose large surfaces to the wind. They are usually lacking in gaudy colours and in perfume. Grasses and pine trees are typical examples of anemophilous plants.
Fig. 204.—Flowers of Black Walnut: Two Pistillate flowers at A, and staminate catkins at B.
In many cases cross-pollination is assured because the stamens and the pistils are in different flowers (diclinous). Monœcious and diœcious plants may be pollinated by wind or insects, or other agents (Fig. [204]). They are usually wind-pollinated, although willows are often, if not mostly, insect-pollinated. The Indian corn is a monœcious plant. The staminate flowers are in a terminal panicle (tassel). The pistillate flowers are in a dense spike (ear), inclosed in a sheath or husk. Each “silk” is a style. Each pistillate flower produces a kernel of corn. Sometimes a few pistillate flowers are borne in the tassel and a few staminate flowers on the tip of the ear. Is self-fertilization possible with the corn? Why does a “volunteer” stalk standing alone in a garden have only a few grains on the ear? What is the direction of the prevailing wind in summer? If only two or three rows of corn are planted in a garden where prevailing winds occur, in which direction had they better run?
