Botany GARDENERS PRACTICAL

PRACTICAL BOTANY for GARDENERS Over 3,000 Botanical Terms Explained and Explored GEOFF HODGE How to use this book LISTING PAGES TECHNIQUE PAGES Background information provides context, Feature pages focus on practical applications, but the core of each section is a list of such as Breaking Seed Dormancy or Pruning, botanical word and terms, with definitions, providing a range of different techniques to making it easy to understand the help the gardener. terminology of botany. BOTANY FOR GARDENERS Seed Dormancy Endogenous dormancy Breaking Seed Dormancy Endogenous dormancy is caused by conditions within the embryo, Many seeds won’t germinate straight away due and can take the following forms. ardeners can manipulate favourable germina- to seed dormancy, and this sometimes prevents Physiological tion conditions to artificially break dormancy germination even when environmental conditions G Physiological dormancy prevents germination until chemical for seed to germinate. There are numerous methods, are optimal. The delay is a survival method that changes occur within the embryo. Sometimes chemicals inhibitors, depending on the species and the reasons behind the gives time for good dispersal. Staggered germina- such as abscisic acid, retard embryo growth so that it is not strong seed dormancy. tion also safeguards some seeds and seedlings enough to break through the seed coat. Some seeds exhibit thermodormancy and are sensitive to either heat or cold; others from suffering damage or death when current Scarification species exhibit photodormancy or light sensitivity. conditions are not conducive to good growth, The seed coat can be rubbed with a file until it and allows some seeds to germinate when Morphological is sufficiently worn away. With small seeds, line a screw-lid jar with sandpaper. Place the seeds in competition from other plants for light and Here the embryo is immature or undifferentiated at the time of seed dispersal. The embryo needs to grow more before the seed the jar and shake. water might be less intense. will germinate, so the seeds ripen after they take in water while on the ground. Cutting or chipping You can cut or ‘chip’ seeds with a hard coat using a Combined sharp knife. Remove just a small, shallow section of BOTANY IN ACTION Some seeds have both morphological and physiological dormancy. BOTANY IN ACTION the coat, preferably near the embryo scar, which is This occurs when seeds with underdeveloped embryos also have where water is absorbed. Don’t cut into the embryo. Combinational dormancy occurs in some seeds, physiological dormancy. They need dormancy-breaking treatments where dormancy is caused by both exogenous and as well as a period of time to develop a fully-grown embryo. Short feature boxes placed throughout the endogenous conditions. Some Iris species, for Hot-water treatment example, have both hard impermeable seeds coats Soaking in water removes the ‘waterproofing’ACANTHUS bear’s breeches and physiological dormancy. Exogenous dormancy material from the seed and allows it to take up water. A few seeds have multiple-stage dormancy and only germinate book demonstrate ways in which the theory Place the seeds in a heatproof, shallow container and in their second spring after periods of both cold and warmth; ash (Fraxinus) is a typical example. The can be broken using the Iris Germanica, Exogenous dormancy is caused by conditions outside the embryo, pour on water that has just gone off the boil. Use warm stratification method. German Iris and can take the following forms. three parts water for one part of seed. Place the dish can be turned into practice, providing Physical in a warm place and leave for 24 hours. The seeds are in a fridge, kept below 5C (41F) for four to 20 This occurs when seeds are impermeable to water or the usually ready to sow when they sink; seeds that float weeks, depending on the species. Check the bag exchange of gases. Legumes are typical examples as they have are non-viable and should be discarded. weekly and remove and pot up germinated seeds. very low moisture content and are prevented from taking up gardeners with practical tips. At the same time, turn and shake the bag to keep water by the seed coat. Cutting or chipping the seed coat allows Cold stratification the seeds aerated. the intake of water. Add tepid water to leaf-mould, composted bark Mechanical and/or coir, or a mixture of each until it exudes Warm stratification Mechanical dormancy occurs when seed coats or other coverings a small amount of water when gently squeezed. Subjecting seed to a warm spell followed by cold can are too hard to allow the embryo to expand during germination. Sprinkle the seeds evenly over the surface. By increase germination. Place the seeds in a bag as volume, use four parts compost to one part seed. Mix above and keep in a warm place at 18-24C (65-75F) Chemical in the seeds to introduce plenty of air. If the mixture for up to 12 weeks, before giving a period of cold This method relies on growth regulators and other chemicals that looks too dense, add sharp grit or vermiculite. stratification. Alternatively, sow in pots and place in are present in the coverings around the embryo. They are washed out of the seeds by rainwater or snow melt and may leach out of Transfer to a plastic bag. Seal and label, and leave in a heated propagator for the required period, then the tissues by washing or soaking the seed. a warm place for two to three days. Chill the seeds place in a cold frame for the winter. 10 11 PRACTICAL BOTANY FOR GARDENERS PLANT PARTS Specialized roots BOTANY IN ACTION Surface roots Roots These roots proliferate close below the soil surface, The roots, or parts of the roots, of many plant species have exploiting supplies of water and nutrients. Where optimal In many respects, the roots are the most important become specialized to serve other purposes besides their In order to function properly, the roots of most growth conditions prevail they commonly become the part of vascular plants. Not only do they anchor primary functions. vascular plants enter into a symbiotic relationship dominant roots. with a soil fungus called mycorrhizae, which comes the plant in place and provide support, they also Adventitious roots from the Greek meaning ‘fungus root’. It is now Taproot absorb water and numerous plant nutrients from possible to buy mycorrhizal fungi, which can be These arise out of sequence from the more usual root formation, An enlarged root that grows downwards, generally straight DIAGRAMS the soil. The roots of many perennial plants are and instead originate from stems, branches, leaves, or old woody added to the soil at planting time to help improve and tapering slightly towards the bottom, from which other also used to store food reserves, allowing them to roots. They are important when propagating plants from stem or root growth and overall plant health, strength and roots sprout laterally. leaf cuttings. Most aerial roots and stilt roots (see below) are survive cold winter weather and other extremes disease resistance. As well as dozens of attractive botanical adventitious. Adventitious roots can form the largest part of the Tuberous roots of environmental conditions. If you look after the root system of some conifers. These roots occur when a portion of a root swells for food or roots of your plants, ensuring the soil is in good Root hair water storage, such as in sweet potato (Ipomoea batatas). condition and well prepared, so that the roots Aerating roots They are a type of storage root, distinct from taproots. illustrations and etchings, the book includes Also known as ‘knee roots’ or ‘pneumatophores’, aerating roots grow and establish quickly, the rest of the plant rise above the ground, especially above water such as in some will also grow strongly. To better understand how mangrove genera. In some plants they have breathing pores for Taraxacum officinale, numerous simple annotated diagrams to to achieve this, it is first necessary to develop an the exchange of gases in swamp or waterlogged conditions. common dandelion understanding of root types and terminology. Aerial roots Plants with taproots, such as the dandelion (Taraxacum officinale), are hard to kill off because the taproot remains Roots that grow entirely above the ground, such as those of ivy clarify technical aspects. in the ground when the top is removed and the plant Root structure (Hedera) or ‘epiphytic’ (e.g. tree-growing) orchids. They provide re-sprouts. support and anchorage, or function as prop roots, as in maize or Mycorrhizae A true root system consists of a primary root and secondary (or as the trunk in the strangler fig Ficus( species). lateral) roots. The primary root is not dominant, so the whole root system is fibrous in nature and branches in all directions to Contractile roots produce an extensive rooting system. This allows it to provide These roots pull bulbs or corms, such as hyacinth and lily, and Propagative roots excellent anchorage and support, and to search out water and some taproots, such as dandelion, deeper in the soil by Roots that form adventitious buds that develop into above nutrients over a large area. expanding and contracting. ground shoots, called suckers, which then form new plants. Coarse roots Stilt roots Lateral root Roots that have undergone secondary thickening and have a Adventitious support roots, common among mangroves, for woody structure. They have some ability to absorb water and example. They grow down from lateral branches, branching nutrients, but their main function is to provide a structure to in the soil. connect the smaller diameter, fine roots to the rest of the plant.

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