It all starts in a seed (Dave’s Garden)

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It all starts in a seed

By Jean-Jacques Segalen (jjacques)
July 6, 2008

Flowers, fruits, trees, bushes, vines, this is usually what you see when walking out in the garden but where do they rise from? What is tiny, rounded, inconspicuous and often poorly considered but which is also absolutely necessary to plants and gardens? Seeds of course and there is no point in arguing on the hen and egg question, seeds are the basis of it all! This matter now set let us get to today’s menu, so what is a seed? Technically speaking it is the result of the sexual propagation of superior plants, the meeting of male gametes contained in the pollen grain and female gametes hidden in the ovule. And this is indeed the sole reason for flowers to bloom, species preservation, sorry for the romantic part (which is an important ingredient of life for us French!) but flowers are not meant just to be offered to your charming lady neighbour, they are here for propagation and will go to any length to achieve this.

Just to get back to the philosophical question of pre-eminence of seeds on plants let us remind that seed is the result of a very long work as the very first plants on Earth, cyanobacterias or blue-green algae which appeared 3.5 billion years ago gave way to ferns some 400 million years ago and the first ovule plants appeared about 340 millions years ago during the carboniferous time. Ferns, which are still very numerous today belong to the ‘inferior plants’ together with mushrooms, lichens, algae and mosses.

Let us take a closer look to seeds now, we just have to hop to the kitchen and find a dry bean. Observe it carefully; it is covered by a tegument or skin which protects it just like our skin does. On one side there is a small hollow with an oval scare, this the hilum or the attachment point of the seed in the pod, which could be compared to our navel. If you have a super eyesight you may see very close to the hilum a real tiny hole, the micropyle that is the trace of the pollen tube that came to pollinate the ovule. Now open the bean; the two fleshy parts are the cotyledons or stockpiles very rich in starch and which will supply the energy to the plantlet until it will be able to produce its own by the mean of photosynthesis. A small germ can also be seen, with a tiny root and minute leaves, this is the embryo which will further develop into the plant itself.

Of course all seeds do not have this look and the shapes, sizes, colours and disseminating strategies are as varied as nature can be. The biggest of all comes from a palm tree which grows only on one island of the Seychelles, the ‘coco-fesse’ (buttock-coco) is produced by Lodoicea maldivica and can reach 20kg, pretty good for a seed! On the other extreme are orchids, some Dendrobium will release powdery seeds weighting 0,000005g (more or less…). But whatever the size or colour, without seeds you would not be reading this article, for how to stay alive without rice, lentils, corn, wheat, barley, grated coconut? Not to mention coffee, pepper, peanut, mustard, nutmeg, almonds and all the nuts? Just think, what was built Mesopotamian civilization? On wheat mostly. What is at the basis of Chinese empire? Rice of course. Sophisticated cultures of the Maya, Aztec and Toltec relied on corn. And the beef many eat is fed on corn or soybean.

Those amazing little things have set up a whole array of highly efficient scattering strategies, adapted to the various places to be conquered and to the various available allies; edible fruits usually rely on bright colours and juicy meat to attract birds. The jacaranda (Jacaranda mimosifolia) and the African tulip tree (Spathodea campanulata) both use light and winged seeds, which will hitch a ride on wind to get to a favourable spot. The butterfly liana (Hiptage benghalensis) has seeds with three wings, which make them fly just like a helicopter, a quite technologically advanced feature! And many of you have blown away the ripe seeds of dandelion sending them away like small parachutes. The coconut, a familiar sight of any tropical shore, has chosen a water-proof, shock-proof packaging as those large seeds may have to fall from 15m high and then float on the sea for weeks before being tossed on a nice sandy beach. The balsam uses a more explosive way, the ripe fruits simply burst open and throw seeds all over the place, a strategy also used by many species of the Acanthaceae family. Another efficient way to disseminate seeds is human or animal hitch-hiking, a short stroll in any wild area in fall will soon get legs, pants or furs covered with sticky seeds using either some gluey stuff or various shapes of spikes, hooks and other tool to grab any passing opportunity.

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About Jean-Jacques Segalen

I am a Parisian born professional horticulturist specialized in tropical seeds producing, set on Reunion island (just between Mauritius and Madagascar) 17 years ago. I spend a lot of time gathering seeds in the wild, the ones I do not grow that is. Also a dedicated Tai-Chi practitioner and tree climber!

Published by

Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.