Germination of seeds
Germination needs three basic conditions: water, air and suitable warmth. First the seed absorbs water and swells, bursting its coat under strong pressure; in water the food in the seed dissolves and starch turns to sugar (which is why sumalak made from wheat sprouts is sweet). Air (oxygen) is needed for respiration, so the soil should be loose and moderately moist. Each species germinates at its own temperature. Many seeds must first pass a dormancy period; apricot, peach and almond stones are hard and germinate slowly, so they are sown in autumn. Large seeds are sown deeper because they hold more food. The radicle enters the soil first, and the budded stem reaches the surface. In a dicot (cotton, bean) the cotyledons come above ground with the seedling, turn green, then use up their food, yellow and fall. In a monocot (wheat, maize) when the food in the endosperm is used up it remains underground like an empty bag. The sprout gradually becomes a seedling and begins to feed on substances made in photosynthesis. Large seeds rich in food give vigorous plants, so seeds are selected before sowing.
Laboratory 6: put bean or wheat seeds in a glass jar with damp sawdust (or cotton wool) and moisten daily; each day remove one seed, dry it and make a collection (10–12 days). Alternative: compare seeds in 3 containers: (1) damp and warm, (2) dry, (3) damp but cold (in a fridge). Safety: do not handle mouldy seeds, throw them away; keep containers clean; wash hands afterwards.