THE ROOT of the matter by Gill Heavens
In the second of her series on how different plant parts work in the garden Gill Heavens looks at the critical role of developing roots When all things are in place, the optimum temperature has been reached and enough water imbibed, our seed is ready to germinate. The radicle, or fledgling root, bursts through the seed coat and takes it first steps, anchoring into its new home. This is an important step, the seedling requires additional nutrients and water for the plumule, which will become the young stem of our plant, to emerge. Only then can they begin to photosynthesise, allowing the plant to mature into a strong and healthy specimens. The radicle pushes downwards into the soil, taking gravity as its indicator, a process known as geotropism. From this small root others will follow, constantly growing and branching. The vulnerable growing point is close to the end of the rootlet and is protected by a root cap. Above this point, protected from damage, fine hairs clothe the root. These tiny whiskers increase the surface area available for absorption. As the systems develop they take on specific form. Some plants produce a mass of delicate roots, concentrated close to the surface. These are known as fibrous roots, grasses being a prime example. They are excellent at preventing soil erosion, the particles of earth are held amongst them, safe from water or wind damage. Some plants are tap-rooted. One, sometimes two, substantial roots travel deep into the ground, providing stability in windy or unstable conditions. They are also experts in mining nutrients from areas unavailable for shallow rooters. Comfrey, carrots and dandelions all fall into this category. It can be hard to rid ourselves of these sturdy characters once introduced into the garden, think of the persistent horseradish, once planted never forgotten! Other plants, including many trees, have a combination of both 50
structures. Initially they send down stabilising tap roots, then develop a horizontal, diffuse system closer to the surface. A combination ensuring the best of both worlds. As Mr Darwin pointed out, over millennia, flora and fauna have adapted to specific conditions and root systems illustrate this perfectly. In order to solve problems peculiar to their environments, plants have modified in their own magnificent ways. Some desert shrubs delve deep to survive, the velvet mesquite, Prosopis velutina, in the Sonoran desert of North America, can travel over fifty meters down in its quest for water. Conversely, many cacti have extremely shallow root systems, widely spread, to take full advantage of any rain that may fall. One problem, two solutions. Members of the family Proteaceae, such as leucadendrons, proteas and banksia, have evolved ingenious proteoid roots to survive in nutrient deficient soils. These seasonally developed roots reach up into the top layer of soil ensuring optimum water and nutrient extraction. This adaption has left these plants particularly sensitive to phosphorus, a chemical in many proprietary fertilisers. They are easily killed with kindness. The genus taxodium, deciduous cypresses from the Americas, grow either on or very close to swamps and other water sources. In order not to “drown” in the oxygen-depleted soils they have developed pneumatophores, sometimes known as “knees” on their horizontal roots. Yes, they breathe through their knees! Roots also serve as food storage, acting as larders for deciduous plants providing nourishment to grow new leaves after a dormant winter. We of course take advantage of some of the tastier of these, including delicious beetroot and parsnips. Tubers are a little more complicated. They grow from either the stem or the root. Root tubers include dahlia and
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