Practical Botany

ContentsChapter 6E x t e r n a l Fac t o r sThe soil128Botany for Beginners6Chapter 2Soil fertility & microorganisms132How to Use this Book7Form & FunctionWatering134A Short History of Botany8Buds38Feeding & nutrients136Roots40Environmental factors142Stems44Influencing environmental conditions148Leaves48Flowers54Seeds & fruit60Chapter 7Bulbs & other food storage organs64PruningHow plants support themselves68Size, shape, flowers, fruit, stems, foliage156Topiary166Bonsai168Chapter 1The Plant KingdomAlgae14Mosses15Lichens & Liverworts16Ferns17Conifers18Flowering Plants20Fungi22RhyncholaeliaChapter 3Inner Workings76Chapter 8OrchidIndex220Bibliography223Credits224Plant naming & common names26PhotosynthesisFamily27Plant hormones78B o ta n y o f t h e S e n s e sGenus28Food & water distribution80Sight17882B o ta n i s t s & B o ta n i c a l29Nutrition & growthSmell180I l l u s t r at o r sTaste184Touch186SpeciesVarieties & cultivars30Chapter 4ReproductionRosa sp.RoseGregor Mendel10Barbara McClintock24Robert Fortune32Prospero Alpini52Richard Spruce70Sexual reproduction88Chapter 9Genetics & plant breeding92Plant Pests & DiseasesAsexual reproduction96Charles Sprague Sargent84Insect pests194Luther Burbank94Other pests198Franz and Ferdinand Bauer106Fungal diseases202Matilda Smith122Chapter 5Viral diseases206The Beginning of LifeCarl Axel Magnus Lindman140Bacterial diseases208Marianne North150Seed germination112Pest & disease resistance210Pierre-Joseph Redouté170Seed dormancy114How plants defend themselves212Vera Scarth-Johnson188Seed sowing116Physiological disorders214James Sowerby200Seed saving120John Lindley218

P r a c t i c a l B o ta n y f o r G a r d e n e r sRootsIn many respects, the roots are the most importantpart of vascular plants. Not only do they anchorthe plant in place and provide support, they alsoabsorb water and numerous plant nutrients fromthe soil. The roots of many perennial plants arealso used to store food reserves, allowing them tosurvive cold winter weather and other extremesof environmental conditions. If you look after theroots of your plants, ensuring the soil is in goodcondition and well prepared, so that the rootsgrow and establish quickly, the rest of the plantwill also grow strongly. To better understand howto achieve this, it is first necessary to develop anunderstanding of root types and terminology.Root structureA true root system consists of a primary root and secondary(or lateral) roots. The primary root is not dominant, so the wholeroot system is fibrous in nature and branches in all directions toproduce an extensive rooting system. This allows it to provideexcellent anchorage and support, and to search out water andnutrients over a large area.Lateral rootRoot hairsPrimary rootRoot tipRoot cap6Pl ant PartsSpecialized rootsThe roots, or parts of the roots, of many plant species havebecome specialized to serve other purposes besides theirprimary functions.b o t a n yi nA c t i o nIn order to function properly, the roots of mostvascular plants enter into a symbiotic relationshipSurface rootsThese roots proliferate close below the soil surface,exploiting supplies of water and nutrients. Where optimalgrowth conditions prevail they commonly become thedominant roots.with a soil fungus called mycorrhizae, which comesAdventitious rootsfrom the Greek meaning “fungus root.” It is nowTaprootThese arise out of sequence from the more usual root formation,and instead originate from stems, branches, leaves, or old woodyroots. They are important when propagating plants from stem orleaf cuttings. Most aerial roots and stilt roots (see below) areadventitious. Adventitious roots can form the largest part of theroot system of some conifers.possible to buy mycorrhizal fungi, which can beAn enlarged root that grows downwards, generally straightand tapering slightly towards the bottom, from which otherroots sprout laterally.Aerating rootsadded to the soil at planting time to help improveroot growth and overall plant health, strength anddisease resistance.Tuberous rootsThese roots occur when a portion of a root swells for food orwater storage, such as in sweet potato (Ipomoea batatas).They are a type of storage root, distinct from taproots.Root hairAlso known as “knee roots” or “pneumatophores,” aerating rootsrise above the ground, especially above water such as in somemangrove genera. In some plants they have breathing pores forthe exchange of gases in swamp or waterlogged conditions.Taraxacum officinale,common dandelionAerial rootsRoots that grow entirely above the ground, such as those of ivy(Hedera) or “epiphytic” (tree-growing) orchids. They providesupport and anchorage, or function as prop roots, as in maize oras the trunk in the strangler fig (Ficus species).Contractile rootsMycorrhizaeThese roots pull bulbs or corms, such as hyacinth and lily, andsome taproots, such as dandelion, deeper in the soil byexpanding and contracting.Propagative rootsCoarse rootsStilt rootsRoots that have undergone secondary thickening and have awoody structure. They have some ability to absorb water andnutrients, but their main function is to provide a structure toconnect the smaller diameter, fine roots to the rest of the plant.Adventitious support roots, common among mangroves, forexample. They grow down from lateral branches, branchingin the soil.Fine or fibrous rootsRoots modified for storage of food (nutrients or water), suchas in numerous root crops. They include some taproots andtuberous roots.Primary roots, usually less than 2 mm in diameter, that areresponsible for water and nutrient uptake. They are usuallyheavily branched and support mycorrhizas (see box). They maybe short lived, but are regularly replaced by the plant.Haustorial rootsThese are produced by parasitic plants, such as mistletoe (Viscumalbum) and dodder (Cuscuta species), that can absorb water andnutrients from another plant.Plants with taproots, such as the dandelion (Taraxacumofficinale), are hard to kill off because the taproot remainsin the ground when the top is removed and the plantre-sprouts.Roots that form adventitious buds that develop into aboveground shoots, called suckers, which then form new plants.Storage rootsStructural rootsThese are large roots that have undergone considerablesecondary thickening and provide mechanical support towoody plants and trees.7

R Polbaenr t hFournt uerne(1x8 x1 x2–x 1– 8x 8x 0)OIur gardens would be much the poorer if itf ga weren’t for the brave exploits of the enigmaticseeds and plants of ornamental or useful kind, notalready cultivated in Britain,” as well as to obtainand notoriously surly botanist, Robert Fortune.information on Chinese gardening and agriculture.During several trips—mainly to China, but alsoHe was especially tasked to find any blue-floweredIndonesia, Japan, Hong Kong and the Philippines—peonies and to investigate the peaches growing inFortune brought back more than 200 ornamentalthe Emperor’s private garden.plants. These were mainly trees and shrubs, but alsoincluded climbers and herbaceous perennials.Each trip enriched Britain’s gardens andgreenhouses with plants covering nearly the wholeHe was born in Kelloe in what is now CountyA to Z of genera, from Abelia chinensis to WisteriaDurham in the northeast of England, and was firstsinensis, including Camellia reticulata, chrysanthe-employed in the Royal Botanic Garden,Edinburgh. Later he was appointed asdeputy superintendent of themums, Cryptomeria japonica, Daphne species,Deutzia scabra, Jasminum officinale, Primulajaponica, and various Rhododendron species.Hothouse Department in the gardenAlthough his travels resulted in theof the Horticultural Society ofintroduction to Europe of many new andLondon (later to be renamed theexotic plants, probably his most famousRoyal Horticultural Society) inaccomplishment was the successfulChiswick. A few months later,transportation of tea from ChinaFortune was granted theposition of the Society’scollector in China.He was sent on his firstjourney in 1843 with littlepay and a request to “collectCaption here please. Caption here please.Caption here please. Caption here please.A great explorer of the Far East in the mid1800s, Robert Fortune returned to Britainwith over 200 species of ornamental plant.He died in London in 1880, and is buriedin Brompton Cemetery in London.“ Th e a r t o f d wa r f i n g t r e e s , a s c o m m o n l y p r a c t i s e dbot h in China an d Japan, is in realit y very simple . . .It is based upon one of the commonest principles ofv e g eta b l e p h y s i o l o g y. A n y t h i n g w h i c h h a s a t e n d e n c yt o c h e c k o r r eta r d t h e f l ow o f t h e s a p i n t r e e s ,a l s o p r e v e n t s , t o a c e rta i n e x t e n t, t h e f o r m at i o no f w o o d a n d l e av e s .”Robert Fortune in Three Years’ Wanderings in the Northern Provinces of China (1847)8Camellia sinensis,Rhododendron fortunei,tea plantrhododendronRobert Fortune was instrumental in introducingtea to India from China, establishing the Indian teaindustry that we know today.Fortune found this plant growing at 3,000 feetin the mountains of eastern China. It was the firstChinese rhododendron introduced to Britain.to the Darjeeling region of India in 1848He became proficient enough with speakingon behalf of the British East India Company.Mandarin that he was able to adopt the localUnfortunately, most of the 20,000 tea plants anddress and move among the Chinese people largelyseedlings perished, but the group of trainedunnoticed, enabling him to visit parts of the countryChinese tea workers who came back with him—that were restricted to foreigners. By shaving hisalong with their technology and knowledge—mayhead andgrowing a ponytail, he was able toLatinplantname,have been instrumental in the later flourishingIndian tea industry.commonnameblend in.effectivelyThe incidents of his travels were related inHe was generally well received on his travels,but did experience hostility and was once threat-Caption herea succession of books, which include Three Years’Wanderings in the Northern Provinces of Chinaened at knife pointantangryA tJourney“ Q byuoe h mob.e r eHei falsot h e r e i s (1847),a quoe h etorthee . TeaQ Countriesu o t e of Chinasurvived killer storms in the se (1857),e r e i f t h e r e i s a q u o t e h e r e .”on the Yangtze River.and YedoQuoted by whatsisnamehere and Peking (1863).9

P r a c t i c a l B o ta n y f o r G a r d e n e r sSeed DormancyMany seeds won’t germinate straight away dueto seed dormancy, and this sometimes preventsgermination even when environmental conditionsare optimal. The delay is a survival method thatgives time for good dispersal. Staggered germination also safeguards some seeds and seedlingsfrom suffering damage or death when currentconditions are not conducive to good growth,and allows some seeds to germinate whencompetition from other plants for light andwater might be less intense.b o t a n yi nA c t i o nCombinational dormancy occurs in some seeds,where dormancy is caused by both exogenous andEndogenous dormancy is caused by conditions within the embryo,and can take the following forms.PhysiologicalPhysiological dormancy prevents germination until chemicalchanges occur within the embryo. Sometimes chemicals inhibitors,such as abscisic acid, retard embryo growth so that it is not strongenough to break through the seed coat. Some seeds exhibitthermodormancy and are sensitive to either heat or cold; othersspecies exhibit photodormancy or light sensitivity.MorphologicalHere the embryo is immature or undifferentiated at the time ofseed dispersal. The embryo needs to grow more before the seedwill germinate, so the seeds ripen after they take in water whileon the ground.CombinedSome seeds have both morphological and physiological dormancy.This occurs when seeds with underdeveloped embryos also havephysiological dormancy. They need dormancy-breaking treatmentsas well as a period of time to develop a fully-grown embryo.endogenous conditions. Some Iris species, forexample, have both hard impermeable seeds coatsand physiological dormancy.Iris Germanica,German IrisExogenous dormancyExogenous dormancy is caused by conditions outside the embryo,and can take the following forms.Gardeners can manipulate favorable germinationconditions to artificially break dormancy forseed to germinate. There are numerous methods,depending on the species and the reasons behind theseed dormancy.ScarificationThe seed coat can be rubbed with a file until itis sufficiently worn away. With small seeds, linea screw-lid jar with sandpaper. Place the seeds inthe jar and shake.Cutting or chippingYou can cut or “chip” seeds with a hard coat using asharp knife. Remove just a small, shallow section ofthe coat, preferably near the embryo scar, which iswhere water is absorbed. Don’t cut into the embryo.Hot-water treatmentACANTHUSSoaking in water removes the “waterproofing”bear’s breechesmaterial from the seed and allows it to take up water.Place the seeds in a heatproof, shallow container andpour on water that has just gone off the boil. UseA few seeds have multiple-stage dormancy and only germinatein their second spring after periods of both cold and warmth;ash (Fraxinus) is a typical example. The can be broken using thewarm stratification method.three parts water for one part of seed. Place the dishPhysicalin a warm place and leave for 24 hours. The seeds arein a fridge, kept below 5C (41F) for four to 20This occurs when seeds are impermeable to water or theexchange of gases. Legumes are typical examples as they havevery low moisture content and are prevented from taking upwater by the seed coat. Cutting or chipping the seed coat allowsthe intake of water.usually ready to sow when they sink; seeds that floatweeks, depending on the species. Check the bagare non-viable and should be discarded.weekly and remove and pot up germinated seeds.Mechanicaland/or coir, or a mixture of each until it exudesWarm stratificationMechanical dormancy occurs when seed coats or other coveringsare too hard to allow the embryo to expand during germination.a small amount of water when gently squeezed.Subjecting seed to a warm spell followed by coldSprinkle the seeds evenly over the surface. Bycan increase germination. Place the seeds in a bagvolume, use four parts compost to one part seed. Mixas above and keep in a warm place at 18–24Cin the seeds to introduce plenty of air. If the mixture(65–75F) for up to 12 weeks, before giving a periodlooks too dense, add sharp grit or vermiculite.of cold stratification. Alternatively, sow in pots andTransfer to a plastic bag. Seal and label, and leave inplace in a heated propagator for the required period,a warm place for two to three days. Chill the seedsthen place in a cold frame for the winter.ChemicalThis method relies on growth regulators and other chemicals thatare present in the coverings around the embryo. They are washedout of the seeds by rainwater or snow melt and may leach out ofthe tissues by washing or soaking the seed.10Breaking Seed Dor mancyEndogenous dormancyCold stratificationAt the same time, turn and shake the bag to keepthe seeds aerated.Add tepid water to leaf-mould, composted bark11

P r a c t i c a l B o ta n y f o r G a r d e n e r sPruningMany gardeners find pruning or cutting backplants confusing, complicated, and even daunting.The purpose of pruning is to influence the wayplants grow. It doesn’t only affect their size—it canalso determine growth, and therefore their shapeand their flower and seed or fruit production.Deeper CutsPlant response to pruningSide shootAdventitious budPruning is a mixture of both art and science: art in making theproper pruning cuts, and science in knowing how and whento prune for maximum results. A little knowledge of plantmorphology and physiology, and how plants grow and respondto pruning, will help you understand pruning much better.In some plants, a single lateral bud may grow away stronglyto produce just one side shoot, which takes on the apicaldominance. In others, two or more side shoots share thedominance and produce bushier growth.NodeThese are only produced when needed (such as after damageor pruning) and there are no dormant buds nearby. They willproduce new leaves or stems, and are often the buds that comeinto growth when hard, renovation pruning is carried out. Insome trees, several buds break at the same point, producing aprofusion of thin stems called water shoots.The points on a stem that hold buds are called nodes. The spacebetween two nodes is called an internode.Vegetative, flower, and fruit budsBudAn embryonic shoot with an immature stem tip.Apical or terminal budPruning approachesSome gardeners constantly cut off shoots, tidying up their plantsto give them a neat overall appearance. Others prefer to cut themback hard, often down to or near ground level. For most plants,the first approach is usually not the best. Constantly tidying upand lightly tipping back plants may make the growthunbalanced, top heavy or lopsided and, if done at the wrong timeof year, will also remove flower buds. For best results, you need tobe somewhere in the middle: hard pruning those plants thatneed it, and just lightly cutting back those that will not re-shootfrom old wood and will die.The uppermost bud on a stem; new extension growth isusually made just below this bud, and all new plant growthcomes from apical buds.A lateral bud that for some reason doesn’t come into growth.Pruning a nearby apical bud is likely to stimulate it into growth,producing new leaves or stems.Lateral budb o t a n yBuds growing on the side of the stem, below the apical bud;also know as axiliary buds.Apical dominanceThe apical bud produces plant growth hormones that suppressthe growth of the buds below the tip. This effect is called apicaldominance. When the apical bud is removed, stopping hormoneproduction, this dominance is lost and the lateral buds at thenodes closest to the cut start to grow, producing new stems andresulting in denser growth.Vegetative buds are usually small and thin and produce leaves.Flower and fruit buds are fatter and contain the embryo flowers.By careful pruning at the right time of year, it is possible tochange vegetative buds into fruiting buds—important whenpruning fruit trees.Dormant budi nA c t i o nIt is possible to break apical dominance in climbersMalus domestica,and wall-trained plants by carefully pulling downapplea vertical shoot training it horizontally. Side shootsare then produced along the shoot, and these aremuch more likely to flower and fruit. This techniqueis particularly useful when training climbers, wallGrowing apple trees as espaliers, and trainingtheir branches horizontally, produces side shootsthat flower and fruit more profusely thanupright trees.shrubs and several trained fruit shapes in order toencourage extra flowering and fruiting instead ofvegetative growth.Apical budb o t a n yi nA c t i o nPruning is not always the answer to reducing thesize of a plant, since it produces stronger regrowth.Lateral budNodeWhen a plant is growing naturally, it produces topgrowth and root growth in balance. When you cutInternodeback the plant it becomes imbalanced and the rootsNodeprovide excess water and nutrients that cause a surgeof new stem and leaf growth. The vigour of the newSide shootgrowth is also inf

Botany in action Short feature boxes placed throughout the book demonstrate ways in which the theory can be turned into practice, providing gardeners with practical tips. Botanists & Botanical illustrators feature spreads profile notable m