Seeds

Seeds of plants can be botanically defined as formations developing from special multicellular ovules, almost always through sexual reproduction, and containing an embryo inside. They serve for reproduction and, when mature, separate from the parent plant. Seeds are characteristic of all so-called seed plants, with gymnosperms having them form on the surface of their producing organs, while angiosperms have them inside fruits. In everyday life, certain fruits are also often called seeds if they contain a single seed and the fruit walls fuse with it (for example, grains of cereals or 'seeds' of carrots). In size, seeds range from 0.1 mm (in orchids, broomrapes) to almost 30 cm in diameter and 9 kg in weight (in the palm Lodoicea). The most important part of a seed is the embryo, which is always multicellular and in most cases sufficiently differentiated into the main organs of the future plant: the rootlet, the stemlet, and several leaflets. In the embryo, especially in its first leaflets, the so-called cotyledons, reserve nutrients are often deposited, causing them to particularly enlarge and predominate over the rest of the embryo mass (for example, in legumes). In other cases, reserve substances are deposited outside the embryo in special nutritive tissue—the endosperm (rarely also in the perisperm, for example, in pepper). Depending on the presence or absence of endosperm, otherwise called albumen (not to be confused with albumen as a substance!), seeds are divided into albuminous (for example, in cereals) and non-albuminous (for example, in legumes). On the outside, seeds are covered by a seed coat made of dense, characteristically constructed cells, which provide good characteristics for microscopic analysis of powdered products. At maturity, most seeds lose water (about 10% water remains) and enter a state of dormancy (anabiosis), without losing viability in such a state often for several years (in cereals up to 10 years or more). With sufficient moisture, temperature, and the presence of oxygen, germination occurs, beginning with the swelling of protoplasmic colloids and the awakening of enzyme activity. Then the embryo begins to develop further, feeding on the reserves deposited in it or in the endosperm. During this process, as a result of intensified respiration, there is significant expenditure of substance, but the volume of the embryo increases due to water intake. Eventually, the seed coat ruptures, and the root establishes itself in the soil, beginning to exist independently through the assimilation of CO₂. Due to the accumulation of reserve nutrients and loss of water during maturation, seeds generally have the greatest nutritional value among all parts of the plant, being the most important source of food for humans and animals. Corresponding to the predominance of one or another group of basic nutrients, seeds are often divided into: 1) starchy—cereals, buckwheat (for example, wheat: starch-68%, fat-1.8%, proteins-10%); 2) oily—sunflower, flax, almond, coconut (for example, walnut: starch and a little sugar-13%; fat-58%, proteins-17%); 3) proteinaceous (for example, lupine: up to 45% proteins, 30% starch and sugar, 5% fat). However, transitions exist between these groups, and for example, soy seeds contain approximately equal amounts of proteins, fats, and carbohydrates (30% each). In some palm seeds, reserve substances are deposited mainly in the form of hemicellulose. In the dry state, their endosperm has the consistency of bone (vegetable ivory from seeds of Phytelephas and others, used for making buttons). Along with food substances, other substances specific to the given plant with poisonous or pharmacological properties often accumulate in seeds, for example, strychnine and brucine—in seeds of Strychnos nux vomica, oil of Croton—in seeds of Croton tiglium, oil of Ricinus—in seeds of Ricinus communis, physostigmine—in Semen Calabar (Physostigma venenosum), etc.