“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.” – George Bernard Shaw
What did you have for breakfast this morning? Perhaps it was coffee and toast or maybe a bowl of cereal. Are you wearing jeans or a cotton shirt? If so, you can thank the seeds that feed and clothe us.
The Triumph of Seeds: How Grains, Nuts, Kernels, Pulses, & Pips Conquered the Plant Kingdom and Shaped Human History by Thor Hanson delves into the central role seeds play in our lives. He says, “seeds are vital everywhere. They transcend that imaginary boundary we erect between the natural world and the human world, appearing so regularly in our daily lives, in so many forms, that we hardly recognize how utterly dependent we are upon them.”
The Origin of Seeds
Over 353,000 kinds of plants, more than 90% of our flora, use seeds to reproduce. But that wasn’t always the case. Over 100 million years ago, the plant world was ruled by giant ferns, horsetails, and club mosses. It was initially thought that seed-bearing plants evolved after the spore-bearing plants of the Carboniferous. A recent theory is that seed evolution began at the same time as spore-bearing plants but on dryer upland areas.
“In some ways, it’s as if seeds evolved in response to the limitations of spores. Instead of banishing sex to the soil, they united parental genes on the mother plant, equipped that progeny with food and dispersed it in a durable protective case that could withstand the elements and sprout when conditions were right. Eventually they even replaced the swimming sperm with pollen, eliminating the need for water.”
Don’t Forget Your Lunch Box
Split an avocado pit and you’ll find plump embryonic leaves enclosing a tiny root and shoot. All it needs is water as it has plenty of food stored in the pit to give it a good start on life. In fact, “months or even years after rooting and leafing out, young avocado trees can still eke out a trickle of energy from the lunches their mothers packed.” Cacao seeds have also evolved to sprout and grow in a dark forest, but they store energy in the form of fat instead of starch.
Grasses take a different approach, providing their offspring with only a small packed lunch, relying on an abundance of seeds to ensure their future. This appears to be a successful strategy as grasses dominate almost every habitat where trees and shrubs cannot survive, including Antarctica.
Space & Time Travellers
Seeds can lie dormant for a surprising length of time before germinating. This means that we can set seeds aside for the next growing season and store them in our cupboards and pantries. The desiccated seed cells have an astonishing ability to regain their structure when the right combination of requirements prompts germination – a change in light, temperature, moisture, or the open flames of a wildfire.
The fluffiness of cotton seeds keeps them buoyant so they can travel by sea for long distances. American cotton species contain the genes of two different African species that must have crossed the Atlantic on separate occasions. The Stealth Bomber was inspired by the Javan cucumber seed, “one of nature’s most efficient airfoils, staying aloft on the slightest breeze and gliding for trips measured not in feet, but in miles.”
Flavourful & Irresistible
“As one of the rarest, sweetest, and most nutritious things in the landscape, ripe fruit can draw animals from far and wide. African elephants trek miles out of their way to find favorite species.” Melons that satisfy thirst often grow particularly well in hot countries.
Seed plants have evolved in step with the animals and birds around them. Wild blueberries ripen in late summer, coinciding “with fall bird migrations and the pre-hibernation fruit-gorging of bears … Fruit-eating birds have developed everything from wider beaks and flexible throats to shorter intestines for processing abundant fruit supplies quickly … Plants, in turn, have learned to tailor their strategies to attract particular types of dispersers. Birds appreciate prominent splashes of red or black (raspberry, blackberry, cranberry, black currant, hawthorn, holly, or yew), but odor is more important for drawing in animals that are color-blind (elephants), nocturnal (bats), or whose noses are sharper than their eyes (tortoises, opossums).”
Attracting seed-dispersing animals is only one side of the equation. Seeds must also be tough. Consider walnuts or hazelnuts. “Their seeds must be attractive enough to be desired, but tough enough so that they can’t be devoured on the spot. A hard shell forces rodents to carry seeds away and gnaw them open later, in the safety of a burrow. Ideally the rodents then forget where they’ve hidden things, or perish before they get around to eating them.”
Other plants employ a chemical defence. Coffee plants treat caffeine as a valuable resource, transferring it to where it is needed most – “The process starts inside young leaves, where caffeine helps fend off insects and snails that prey on tender foliage. But as those leaves grow and toughen, the plant withdraws much of that caffeine and redirects it to protect flowers, fruits, and the developing seeds.”
Caffeine fends off attackers, but it also prevents germination so it must sprout quickly away from the caffeinated part of the bean. “As the seedling gets bigger, caffeine leaks from the dwindling endosperm and spreads into the surrounding soil, where it appears to curb the growth of nearby roots and stop other seeds from germinating.”
Nature Reading by Canadian Authors [EcoFriendly West]
Photo credit: https://www.flickr.com/photos/apmckinlay/48824173026 (hollyhock seeds)
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