=805. Purpose of the flower.=—While the ultimate purpose of all plants is the production of seed or its equivalent through which the plant gains distribution and perpetuation, the flower is the specialized part of the seed plant which utilizes the food and energies contributed by other members of the plant organization for the production of seed. In addition to this there are definite functions performed by the members of the flower, which come under the general head of plant work, or flower work. =806. The calyx, or the sepals.=—These are chiefly protective, affording protection to the young stamens and carpels in the flower bud. Where the corolla is absent, sepals are usually present and then assume the function of the petals. In a few instances the calyx may possibly ultimately join in the formation of the fruit (examples: the butternut, walnut, hickory). =807. The corolla, or petals.=—The petals are partly protective in the bud, but their chief function where well developed seems to be that of attracting insects, which through their visits to the flower aid in “_pollination_,” especially “_cross pollination_.” =808. The stamens.=—The stamens (= microsporophylls) are flower organs for the production of _pollen_, or _pollen-spores_ (= microspores). The _stalk_ (not always present) is the _filament_, the _anther_ is borne on the filament when the latter is present. The anther consists of the _anther sacs_ or _pollen sacs_ (microsporangium) containing the pollen-spores, and the _connective_, the sterile tissue lying between and supporting the anther sac. The stamens are usually separate, but sometimes they are united by their filaments, or by their anthers. When the pollen is ripe they open by slits or pores and the pollen is scattered; or in rarer cases the pollen mass (_pollinium_) is removed through the agency of insects (see Insect pollination, Chap. XLIII). =809. The pistil.=—The pistil consists of the “_ovary_,” the _style_ (not always present), and the _stigma_. These are well shown in a _simple pistil_, common examples of which are found in the buttercup, marsh marigold, the pea, bean, etc. The simple pistil is equivalent to a _carpel_ (= macrosporophyll), while the _compound pistil_ consists of two or several carpels joined, as in the toothwort, trillium, lily, etc. The _ovary_ is the enlarged part which below is attached to the receptacle of the flower, and contains within the _ovules_. The _style_, when present, is a slender elongation of the upper end of the ovary. The _stigma_ is supported on the end of the style when the latter is present. It is often on a capitate enlargement of the style or extends down one side, or when the style is absent it is usually seated directly on the upper end of the ovary. The stigmatic surface is glutinous or “sticky,” and serves to hold the pollen-spores when they come in contact with it.