FLOWER, that portion of the anthophytous plant which consists of the organs of sexual reproduction, with the accompanying envelopes, if present. Popularly this term is applied only when one or both sets of floral envelopes are conspicuous, or even to showy groups of flowers. The flower consists of an axis, fre quently very much shortened or otherwise modi fied, called the torus. From this there arise typically, in basipetal succession, the pistil (or pistils), stamens, petals and sepals. In many types of flowers, however, one or more of these sets of organs may be lacking. Production of seeds follows the application of pollen, pro duced by the stamens, to the pistil, within which the seed or seeds are developed.
Detailed The pistil may be simple, i.e., consisting of but one megasporo phyll (carpel), in which case the number of pistils in the flower may be more than one, or compound, i.e., consisting of two or more par tially or completely united megasporophylls. Ex cept in monstrosities never more than one com pound pistil occurs in a flower. The pistil usually shows two or three fairly well marked portions, the ovary, style and stigma, the second often being absent. The ovary is the enlarged basal portion of the pistil and is hollow, con taining the ovule or ovules; the stigma is a specially modified region, usually apical or nearly so, to which the pollen grains adhere and find suitable conditions for their germination leading to the fertilization of the ovules; the style is the slender, elongated upper portion of the pistil situated, when present, between the ovary and the stigma, thus raising the latter up, away from the ovary. The ovary may 'possess one cavity or locule ("one-celledp ovary) or several. The latter case occurs only when the pistil is compound. The stigma and style may be single or several in number. A 'single style may possess several stigmas. The ovules may be numerous or but one and attached at various points on the interior of the .ovary. These regions of attachment are called placenta. The there are component megasporophylls (parietal placenta.), e.g., violet. In the Pink family the placenta is axial, as in the lily, but the thin septa are dissolved early in the growth of the pistil, so that the placenta seems to have arisen free in the centre of the ovular cavity (free central placenta). The ovules are the future
seeds. They consist of a central body, called the nucellus, in reality a sporangium (mega sporangium) surrounded by one or two protec tive coats (integuments), which enclose the nucellus entirely, except for a small apical open ing (micropyle). The ovule may he sessile or provided with a short or long stalk (funiculus). It may be straight or bent back upon the funi culus or curved. It may arise from the bottom of the ovary (basal), or from the sides, or may hang from the top (suspended). Within the nucellus are produced typically four spores (megaspores), one of which develops into a megasporophylls are open in the very young flower buds but gradually fold together and unite by the time of opening of the flower. The ovules are attached at the united edges. In a simple pistil the ovary has but a single cavity and the ovules are attached to only one placenta, the style is single and the stigma also. In a compound pistil the component megasporophylls may be closed, as in simple pistils and then united by their adjacent outer faces, forming a pistil with as many locules as there are carpels, with the ovules in the central angles (Placenta e.g., lily, or they are joined edge to edge, forming a one-loculed ovary with as many placenta against the outer wall as rudimentary female plantlet (gametophytc), the so-called embryo sac, entirely enclosed within the ovule. Within this is produced a single egg. The pollen grain (microspore) germinating upon the stigma produces a long tube contain ing several cells (representing a small male plantlet or gametophyte) which grows down through the style into the cavity of the ovary and enters the ovule through the micropyle (rarely through the funicular or achalazaP) end). On reaching the embryo sac a sperm nucleus is set free which fertilizes the egg. The latter now grows and divides, produc ing the embryo plant for the new generation. This is at first nourished by the embryo sac which may develop into a considerable mass of tissue (endosperm), taking its nourishment in turn from the tissues of the ovule. As the seed matures this endosperm may be all con sumed or part of it may remain, resulting in respectively exalbuminous or albuminous seeds.