Fertilization takes place in the ovule and results in the formation of a seed. At the same time the fertilized flower sheds its petals, and the ovary containing the seed or seeds develops into a fruit.
Fruits are said to be hard, dry, soft or succulent. The dry, hard hazel nut and the soft, succulent tomato are unlike in appearance but alike in origin. Both are fruits developed from a matured ovary, with their seed enclosed in a fruit wall known as the pericarp.
The fruit serves as a nursery for the maturing seed, and a protective covering and a mechanism for the seed’s dispersal when ripe. Both fruits and their seeds are wondrously modified for the act of dispersal in various ingenious ways.
DISPERSAL OF SEEDS
The simplest device adopted by several many-seeded dry fruits, such as, beans and , is a pod which splits when ripe so that the seeds are shaken out by the wind. Poppies form a capsule with small holes near the cap and when the head sways in the wind, or is knocked, the ripe seeds are shaken out and scattered. Plants such as broom, violas and gorse eject their seeds from pods forcibly, and the pods curl back.
Many seeds, such as the plumed seeds of dandelions, clematis and willow-herb and the winged seeds of sycamore, ash and birch, are dispersed by air currents. Other plants disperse their seeds by letting them fall on flowing water. Some seeds have hooks or barbs by which they can attach themselves to passing animals and be carried afar. The seeds of cleavers and agrimony are transported in this way. Other seeds, such as those of colchicum, are sticky and travel by adhering to the feet of animals or birds. Food-storing animals, such as squirrels, move tree seeds or nuts, and ants are often responsible for removing and transporting seeds of broom and gorse.
The succulent fruits, such as berries (gooseberries, blackberries, ivy) and drupes (stone fruits), have seeds resistant to digestion which travel in and through the animals and birds that eat them.
The so-called false fruits, such as apple, pear, strawberry, rose hip and haw, are largely succulent developments of the receptacles of their flowers. They carry hard, dry, one-seeded fruits known as achenes (on the outside in the case of the strawberry), and these achenes may also pass without damage through the digestive tracts of animals or birds.
It is wise to thwart the dispersal of weed seeds in the garden by controlling thebefore they come into flower.
Many garden plants set seed freely and it is tempting to harvest them when ripe to save for future sowing. But such seeds are only likely to give plants similar to the parent plant or to breed true to type when they are the result of self- or cross-pollination between plants of the same species or strain.
Among vegetables, for instance, it is usually safe to save seeds from peas,, and runner beans where they are grown in rows with some distance between varieties. Lettuce and tomatoes are self-pollinating and the seeds from first-class plants can be saved. like carrots and , when grown for seed, need to be isolated according to variety, and the garden must be kept free of weeds of the same flower family (Cruciferae) if seeds are to be true to the parent type. Among brassica crops cross-pollination is rife and seed from garden-grown plants is hardly ever worth saving.
Onions andyield good seed in their second year, but if they are being grown for seed it is necessary to isolate them according to variety to prevent cross-pollination.
In the flower garden, seeds from cherished plants grown more or less in isolated groups of their own kind often give rewarding plants. Many annual species yield useful seed, but some strains and varieties of hybrid flowers are so highly bred as to give only mixed results from home-saved seed, while some are even sterile.
It is tempting to experiment with cross-pollination, though hybrid seed will yield progeny of variable quality. This is the beginning of the high adventure of hybridization, the path along which finer and better plants may be found.