Fig. 59.—Cross section through a Wallflower bud. Sep, sepals; Pet, petals; lg.st., anther of a long stamen; sh. st., anther of a short stamen; pol.sac., pollen sacs; Ov, wall of ovary; Ovl, ovule. (× 8.) When the sepals and petals are removed, there remain standing on the receptacle six stamens surrounding a centrally-placed pistil (Fig. 58, D). The stamens are the male part, and the pistil is the female part, of the flower. Each stamen consists of a greenish stalk or filament, surmounted by a yellow boat-shaped body called the anther. The anther is a box with four compartments (Fig. 59). When it is ripe, each compartment contains an enormous number of tiny, yellow grains called pollen grains; and when the anther bursts (as it does as soon as the flower opens) its inner face is covered by the yellow dust of the pollen. The pistil bears a rough resemblance to a slender bottle, and consists of three distinct parts. The neck of the “bottle,” called the style, is short in the wallflower, and differs from an ordinary bottle-neck in being solid instead of tubular. At the top of the neck, where the cork would come in a real bottle, is a body called the stigma. The stigma of the wallflower pistil is hairy, notched, and slightly sticky, from the presence of a sugary solution which forms [Pg 92] upon it. The part of the pistil, corresponding to the body of the bottle, is the ovary. It contains four rows of little white ovules, which are destined to become seeds capable of growing up and forming new wallflower plants. The relations of the parts of the flower are well seen in Fig. 59. Fertilisation.—In order that an ovule may become a seed, its contents must mix with the contents of a pollen grain. The fusion of the two constitutes fertilisation. For fertilisation to take place, the pollen grain must first of all gain access to the stigma of the pistil. If this be prevented the flowers will wither without forming ripe seeds. (This may be proved easily by Expts. 18, 3 and 21, 2.) The sugary solution at the top of the stigma stimulates the pollen grains to growth, and each puts out a long tube which grows down the style. The living matter of the grains keeps near the tips of the tubes as these continue their journey down the style. At length the tubes enter the ovary and find the ovules. Each ovule has at one end a minute pore (the micropyle—p. 6), and a pollen tube finds this and enters it. The living matter of the pollen tube fuses with that of the ovule in the neighbourhood of the pore, and fertilisation is effected. It is now easy to understand that the comparatively insignificant stamens and pistil are the all-important parts of a flower.