Let us see what a flower really is. Take, for example, a buttercup, cotton, tobacco, or plum blossom (see Figs. 31 and 32). You will find on the outside a row of green leaves inclosing the flower when it is still a bud. These leaves are the _sepals_. Next on the inside is a row of colored leaves, or _petals_. Arranged inside of the petals are some threadlike parts, each with a knob on the end. These are the _stamens_. Examine one stamen closely (Fig. 33). On the knob at its tip you should find, if the flower is fully open, some fine grains, or powder. In the lily this powder is so abundant that in smelling the flower you often brush a quantity of it off on your nose. This substance is called _pollen_, and the knob on the end of the stamen, on which the pollen is borne, is the _anther_. [Illustration: FIG. 32. A PLUM BLOSSOM] The pollen is of very great importance to the flower. Without it there could be no seeds. The stamens as pollen-bearers, then, are very important. But there is another part to each flower that is of equal value. This part you will find in the center of the flower, inside the circle of stamens. It is called the _pistil_ (Fig. 32). The swollen tip of the pistil is the _stigma_. The swollen base of the pistil forms the _ovary_. If you carefully cut open this ovary you will find in it very small immature seeds. [Illustration: FIG. 33. STAMENS _a_, anther; _f_, filament] Some plants bear all these parts in the same flower; that is, each blossom has stamens, pistil, petals, and sepals. The pear blossom and the tomato blossom represent such flowers. Other plants bear their stamens and pistils in separate blossoms. Stamens and pistils may even occur in separate plants, and some blossoms have no sepals or petals at all. Look at the corn plant. Here the tassel is a cluster of many flowers, each of which bears only stamens. The ear is likewise a cluster of many flowers, each of which bears only a pistil. The dust that you see falling from the tassel is the pollen, and the long silky threads of the ear are the stigmas. [Illustration: FIG. 34. A TOMATO BLOSSOM] Now no plant can bear seeds unless the pollen of the stamen falls on the stigma. Corn cannot therefore form seed unless the dust of the tassel falls upon the silk. Did you ever notice how poorly the cob is filled on a single cornstalk standing alone in a field? Do you see why? It is because when a plant stands alone the wind blows the pollen away from the tassel, and little or none is received on the stigmas below. [Illustration: FIG. 35. CUCUMBER BLOSSOMS]