Seed Structure and Germination

Seed Structure Spelling list: –Seed Coat (Testa) –Endosperm –Embryo –Cotyledon –Epicotyl /Hypocotyl –Radicle –Micropyle

Seed Coat The seed is the product of a ripened ovule after fertilization. The seed coat protects the embryo sac, they can be of varying thicknesses, depending on the plant seed.

Endosperm Made up of two parts – the starch storage area –the aleurone layer (the covering layer) which stores protein in abundance.

Embryo The embryo is what forms the new plant once the opportune conditions are present. Before a seed can sprout the embryo needs to be fully developed.

The Cotyledon The Cotyledon is the first leave that germinates from the seed. The embryo has 1 cotyledon if the plant is a Monocot and 2 cotyledon (Dicotyledons) if the plant is a dicot.

Epicotyl /Hypocotyl This is the basis for the plant’s stem. It is known as the Epicotyl above the cotyledon(s), a Hypocotyl below seed. These grow upward in response to light.

The Radicle This is the part of the seed where the root develops

Seed Dispersal There are five general ways a seed disperses its seeds. 1.Gravity 2.Animals 3.Wind 4.Water 5.Force Seeds can be dispersed by one or a combination of these methods.

Gravity If they have a tough outer shell, they may roll some distance from the parent plant. The higher up the tree they are, and the larger they are, the further they can roll. If they have a soft skin, they may break open when they hit the ground and the individual seeds may be scattered. On lower-growing plants, many fruits and seeds are also heavy enough to fall to the ground without any other help. When they reach the ground, some seeds are taken further from the parent plant by animals or water.

Animals Animals will eat seeds and then deposit them in their dung away from a parent plant Or seeds have adapted burs to stick to animals coats so that the animal will carry the seed away.

Wind Wind is another way of dispersing seeds. A sycamore seed has a wing shape so that the wind will carry it far from the parent tree. A dandelion has much the same structure but it is light and fluffy so that the wind can carry it far.

Water Although seeds of plants that grow in water are obviously spread by water, there are many other ways in which water plays a part in dispersing seeds. Plants which grow beside water often rely on water to transport their seeds for them. They may produce light seeds which float, or there may be fluff that helps buoyancy. Trees found on tropical beaches often have their seeds carried there by the sea. They have woody, waterproof coverings which enable them to float in the salty water for long periods. Coconuts are well-known travelers.

Force Force relies on the effect of evaporation of water from the seedpod, so this method of seed dispersal usually takes place in the sun. The side of the seedpod facing the sun dries out more quickly than the side in the shade, causing the pod to buckle and pop open. The seedpods then curl up like animal horns, sending the seeds flying.

Germination Defined as the emergence of the radicle through the seed coat Depends on the interplay of many internal and external factors

Temperature 1.Cool temperate tolerate plants –Plants native to temperate zones(4.5°C; optimal: 25°-30°C) 2.Cool moist plants –Plants native to Mediterranean type climates (no >25°C) 3.Warm temperature plants –(10°-15°C) 4.Alternating diurnal temperature cycles (warm soils during the day, cool at night)

Oxygen Germinating seed are very metabolically active - respiration is occurring at high rates breaking down storage materials and sugars and converting them to other forms more useful to the seed. Oxygen is necessary for this process! Limited O 2, such as in clay soils or flooded conditions, germination is delayed or viability lost

Light Epiphytes – light must be present in order to germinate Physiological dormancy – many plants with small seeds need light to overcome dormancy. Often found near soil surface (lettuce, conifers) Darkness is necessary for some plants, i.e. cacti, as it is a sign of moisture in desert environments Photoperiod – woody, temperate zone species require particular day lengths

Requirements for Germination Viability Storage Environmental Conditions (moisture, temperature, oxygen, light) Seeds ability to overcome dormancy

Germination Stages 1.Activation 2.Digestion and Translocation 3.Seedling Growth Epigeous germination (left); hypogeous germination (right)

Sources How seeds spread.unknown.Seed Dispersal. April Stern, Kinsley R. Introductory Plant Biology. Wm. C. Brown Publishers, Iowa

To Mr Clerke My Name is Simran I think I love you <3