Seeds & Science

What is a seed? 

To quote George Bernard Shaw in ‘The Vegetarian Diet According to Shaw’ in 1918:

“Think of the fierce energy concentrated in an acorn! You bury it in the ground and it explodes into a giant oak! Bury a sheep and nothing happens but decay.”

Actually botanically and scientifically there are two flaws in the above quote.

Firstly an acorn from an oak tree is a nut and secondly the decomposing sheep provides an abundance of nutrients back into the soil through the action of bacteria and fungi that inhabit the soil. The subsequent nutrients released support plant life in addition to the carbon dioxide, water, resynthesized carbon compounds and energy. However his idea of seeds being a ‘fierce energy’, a capsule of potential or grenade containing life itself is wholly accurate. The seed is the only time in the life of a plant when it is mobile.

Where do seeds come from?
In the plant kingdom the Angiosperms which are the vascular flowering plants and Gymnosperms are the two families that produce seeds. Gymnosperms are vascular plants that bear “naked” seeds—that is, seeds not enclosed in fruit. The most well-know group of gymnosperms are conifers (such as pine trees and fir trees.) Conifer seeds are contained within cones instead of flowers and are not visible until mature. The Angiosperms account for nearly 80% of all plants even though they have evolved relatively recently and they produce flowers and fruit. The flowers are the organs of sexual reproduction and the pollen from one flower must reach the female parts of another flower (stigma, style and ovary) in a process called pollination which is the plant equivalent of mating! Fertilization occurs when the male gamete in the pollen fuses with the ovules in the ovary which subsequently develops into the seed. The seed consists of the developing embryo plant and a food store of nutrient dense tissue which is the energy source when germination takes place. This ‘fierce spark’ is a portable capsule containing everything the embryo plant needs to survive and ultimately thrive before it emerges from the soil, develops a leaf and embarks on photosynthesis.

Why are seeds produced?
The human diet relies upon seed from breakfast through to dinner everything you have eaten, not just plant based foods, has involved seeds which are an integral part of our life.

The successful colonization of land by plants has been primarily due to the success in seeds being able to spread and conquer new areas. In this way the plant avoids competition with its own seedlings for light, water and minerals which are integral for its survival.

The image image below illustrates the astounding diversity of size, shape, texture and weight of seeds found in nature. This diversity hasn’t just happened by chance but evolved due to the method by which the seed is spread/ dispersed.

Image © Kevin Widdowson

The ability to travel by themselves or via animal vectors has given seeds access to new habitats and enduring success. Many plants rely on wind to help them spread their seed as far as possible whilst others have produced special adaptations so that they can be carried by or in animals, water or by producing explosive seed pods! Have a look at the photos and decide the method of seed dispersal for the various seeds.

• The seeds of a dandelion are light, feathery with parachute type structures which enables them to spread widely and colonize new territory.

• The bladder senna makes use of the force of gravity to spread its seed and ultimately does not travel so far from the mother plant.
• The Hogweed is another plant along with sycamore and maple, which have winged structures, that utilises the wind. The black popular has seeds that look similar to cotton wool and they too float through the air to a new destination.

• The Squirting cucumber plant and gorse have adopted an exploding mechanism whereby the fruit explodes out its seeds.
• Goose grass, burdock, blackberries, strawberry seeds are dispersed by animals. The burdock seeds have small hooks that attach themselves to the coats of passing animals. Blackberries and strawberries rely on birds ingesting their sweet and fragrant fruit ( a method of attraction) and they survive the digestion process just like tomatoes and arrive in their new destination wherever the bird poops them out! The production of such berries is a heavy investment in terms of nutrient requirements by the plant but the rewards are justified by the area the seeds are dispersed in and the ultimate survival of the plant species..

• Coconuts can float for weeks or even months on ocean currents which will carry them hundreds of miles from completion with their parents or other coconuts.

• Coco de mer or double coconut is the largest seed in the world and extremely rare, found on just two islands in the Seychelles, though we do have one in the Garden Museum! The size and mass of the seed limits the area that the seed can travel and it is usually found growing close to the parent tree. It can grow underground up to 30 m away from the parent tree before it emerges and this ensures it receives adequate water, minerals and light required for growth.

Whatever the method of dispersal the seed is portable, protected by its seed coat and well nourished. Seeds are dormant until the time is right, the conditions are right to trigger germination. For some this may be after the passage through an animal, a cold spell or even a fire. Many can remain in the soil for decades and this feature of dormancy is unique and allows the diversification and specialization of over 350,000 kinds of plants that use seeds to reproduce.

• The oldest seed found and germinated was from a date palm seed from Masada in Israel which was dated to be 2,000 years old.
• The largest flowers in the world are those of the Rafflesia which grows in the rainforests of South-East Asia. The fleshy fruits are the size of grapefruits and approximately 15 cms across. The seeds of this fruit are dispersed by elephants who are drawn to the yeasty smell of the fruit pulp. The fruits themselves have very little flesh and a large stone which is too large to be eaten by any animals other than the Asian elephant. Research revealed that areas where the Asian elephant, which is an endangered species, is not found anymore correlated with a decline in that area of the number of Rafflesia plants.

The Seed Market by Rumi (c1270)
Can you find another market like this?
Where, with your one rose
You can buy hundreds of rose gardens:
Where,
For one seed
You get a whole wilderness?

Images published with thanks to Kevin Widdowson.
Images must not be printed or reproduced 

What is a nut?
In botanical terms a nut can be defined as a seed that has a very hard outer shell that does not open and release the seed when mature. The nut develops from more than one carpel which is the female reproductive organ. It can be described as a one-seeded fruit with a hard woody wall.

Nuts are very expensive for plants to make in terms of nutrient and energy expenditure as they are rich in oils, proteins and minerals and vitamins. This makes them for humans to eat in terms of being high in dietary value but for the plant the trade off is that they can be carried, by animals such as birds and squirrels, to new territories and the species can flourish.

• Did you know that the peanuts are not really nuts? They are legumes and develop underground and are the seeds of a tropical pea-like annual plant and are referred to as groundnuts. Many farmers grow crops of groundnuts primarily as a source of oil which is used widely in the food industry.
• Pecans, sweet chestnuts, beech, acorns and hazelnuts are considered to be true nuts. Cashew, almond and pistachio are not classified as nuts but as ‘drupes’. Drupes can be defined as fruits that are fleshy on the outside and contain a shell covering a seed inside. Mangoes and peaches are also considered to be drupes in that we are able to eat the juicy flesh and not the shell and seed inside.
• The Maiden hair tree or Ginkgo biloba does very rarely sets fruit in the UK but in the Far East it produces round almond shaped nuts which are eaten at Chinese weddings.
• Nutmeg is only ever used as a spice and is the kernel of the nut mace and when ripe rattles when ripe.
• Cobnuts, a relative of hazel, have been grown commercially in the UK since the 18th century. The Kentish Cob is one of the most well known varieties and developed by Mr. Lambert of Goudhurst in Kent in the 1800s. A plat is the name given to a cobnut orchard which is a natural habitat for the declining dormouse.
• Nuts like fruit have had a strong association with love. In the past brides in Devon were met by an old lady as they came out of the church and given a bag of hazelnuts which were thought to promote fertility! Interestingly in many countries a good nut harvest was an indication of an increase in birth rate in the coming year.
• Folklore also said that if you wanted true love you had to find a nut with two kernels and share it with the partner of your dreams. Happy eating!