Seeds are the embryos of new plants. They are contained within a protective outer covering called a husk or seed coat. Inside the seed is the embryo, which is made up of cotyledons and a radicle.
This mix can be used to start a new lawn or overseed a patchy one. Before sowing, the soil needs to be properly prepared by mowing, raking and removing debris.
Definition
Seeds are the rudiments of a new vegetable plant, containing an embryo and supply of food reserves wrapped in a protective shell or seed coat. Seeds are generally dormant until they are sown and the conditions for their germination are met.
They are the primary source of most of the world’s food, including cereals and legumes. They also provide most of our cooking oils, many spices and some important food additives.
In agriculture, “growing true to seed” refers to plants that produce seeds that are genetically identical to the parent plant. Open-pollinated seeds such as heirlooms, and hybrid seeds produced from cross-pollination are examples of this.
Stratification, the process of subjecting seeds to periods of cold and warm temperatures before planting, breaks down physiological dormancy. This method is used for a number of crops to increase their chances of germination. Stratification can be done artificially or by subjecting seeds to natural cycles in temperature, such as during a typical annual cycle.
Origin
The seed was one of the great evolutionary innovations that allowed vascular plants to dominate biological niches on land. Its development also eliminated the requirement that sperm cells swim through environmental water to reach the megagametophyte, opening up many new biological possibilities for plants.
A seed is a mature ovule that contains an embryo. The ovule consists of a diploid megasporangium (nucellus) with a single functional megaspore, surrounded by diploid covering layers, the integuments, that evolve into the seed coat. An apical opening in the megasporangium that later becomes the micropyle facilitates wind pollination and ovule fertilisation.
Plants that reproduce with seeds are called “angiosperms” or “gymnosperms”. Angiosperms grow their seeds inside fruits, such as tomatoes or apples; gymnosperms, such as pine trees, grow their seeds inside hard cones. Other plants use spores to reproduce. Spores require more moisture than seeds, so they only work in wet places, such as along lakes and rivers. This limits the range of plants that can grow using spores.
Functions
Seeds serve several functions for the plants that produce them, including nourishment of the embryo, dispersal to a new location, and dormancy in unfavorable conditions. They also represent the basic input for agriculture upon which many other inputs depend.
The outer layer of a seed is known as the seed coat, and it provides protection and moisture retention. Inside the seed is a food source called the endosperm, which stores starch, sugars and proteins that provide energy to the embryo until it germinates.
During germination, parts of the embryo break out of the seed coat. One of these parts, the radicle, grows downward to anchor the plant firmly in the soil. The other part, the cotyledons, grows upward to form the first leaves of the plant.
Oxygen is necessary for cellular respiration during the germination process. However, the seed cuticle and the lipid-containing aleurone layer of the endosperm act as barriers to oxygen uptake. In a study of barley seeds, researchers found that the activity of DNA repair enzymes could help overcome these barriers and allow oxygen to reach the embryo (Adamski et al., 2004).
Distribution
Seed distribution involves moving packaged seed from the store where it is held following processing and packing to farmers. This may be a single step, if sales are made directly to farmers, or a series of steps involving intermediate wholesalers and retailers. A contract will exist between the supplying organization and the dealer, covering not only product delivery but also various administrative and record keeping obligations.
Generally, farmers purchase seed only shortly before the time to plant, making it difficult to plan a distribution system to meet their needs. In some cases this can lead to shortages and disappointment for the customer, especially if they cannot get the variety they want.
Focus group discussions with farmers have found that the availability of improved varieties, household income, educational level, extension contact and access to credit influence their selection of formal seed distribution systems. They also affect the choice of methods they use to generate off-farm income and seed saving.
