Typical germination process
As soon as the embryo begins to grow out of the seed, i.e. germinates, the plant is vulnerable to damage from cold or drought. Therefore, the seed must have a mechanism to prevent germination when poor growing conditions prevail. Dormancy is a period during which very little activity occurs in the seed, other than a very slow rate of respiration. Seeds will not germinate until dormancy is broken. A thick testa prevents water and oxygen, essential in germination, from entering the seed. Gradual...
Plant modifications to extreme conditions see also p
A survey of plants worldwide shows what impressive structural and physiological modifications they possess to survive in demanding habitats. A few examples of British species are described here. Marram grass Ammophila arenaria living on sand dunes controls water-loss by means of leaf lamina which in cross-section is shown to be rolled up. It also possesses extremely long roots see page 78 . The yellow water lily Nupar lutea shows the following modifications leaves with a thin cuticle but with...
Bees in pollination
The well-known social insect, the honey bee Apis mellifera , is helpful to horticulturists. The female worker collects pollen and nectar in special pockets honey baskets on its hind legs. This is a supply of food for the hive and, in collecting it, the bee transfers pollen from plant to plant. Several crops, such as apple and pear, do not set fruit when self-pollinated. The bee therefore provides a useful function to the fruit grower. In large areas of fruit production the number of resident...
Plant form in design
Plant form as individual plants or in groups is the main interest for many in horticulture who use plants in the garden or landscape. Contrasts in plant shapes and sizes can be combined to please the eye of the observer. The dominant plant within a garden feature is usually a tree or shrub chosen for its special striking appearance, or specimen plant. In a large feature, it may be a Betula pendula silver birch tree growing up to 20 m in height with a graceful form, striking white bark, and...
Identifying plants
A flora is a text written for the identification of flowering plant species. Some flora use only pictures to classify plants. More detailed texts use a more systematic approach where reference is made to a key of features that, by elimination, will lead to the name of a plant. Species are described in terms of their flowers, inflorescences, stems, leaves and fruit. This description will often include details of shape, size and colour of these plant parts. Flowers. The number and arrangement of...
Application of herbicides and pesticides
This subject is described in detail in machinery texts. However, certain basic principles related to the covering of the leaf and soil by sprays will be mentioned. The application of liquids and wettable powders by means of sprayers may be adjusted in terms of pressure and nozzle type to provide the required spray rate. Cone nozzles produce a turbulent spray pattern suitable for fungicide and insecticide use, while fan nozzles produce a flat spray pattern for herbicide application. In periods...
Divisions of the plant kingdom
Figure 4.2 Four multicellular plant divisions horsetail with horticultural significance Figure 4.2 Four multicellular plant divisions horsetail with horticultural significance Mosses and liverworts. Over 25 000 plant species which do not have a vascular system see p92 are included in the divisions Bryophyta and Hepatophyta. They have distinctive vegetative and sexual reproductive structures, the latter producing spores that require damp conditions for survival. Many from both divisions are...
Vegetable production
The choice of cultivar is an important decision that has to be made before growing starts. There are many possibilities for each crop, but a major consideration is the need for uniformity. Where this is important, e.g. for 'once over harvesting' or uniform size, then F1 hybrids are normally used even though they are more expensive see p144 . Required harvesting dates affect not only sowing dates but the selection of appropriate early, mid-season or late cultivars. Other factors for choice...
Other effects on soil
Beneficial soil organisms see p320 are affected by soil acidity and liming. A few soil-borne disease-causing organisms tend to occur more frequently on lime deficient soils see clubroot , whereas others are more prevalent in well-limed soils. Calcium sometimes improves soil structure and soil stability. It is probable that this is mainly because it encourages root activity and creates conditions favourable for decomposition of organic matter, yielding humus see p326 . Free lime in clay soils...
Deficiencies
Simple deficiencies are those in which too little of the nutrient is present in the growing medium. Most soils have adequate reserves of trace elements, so simple deficiencies in them are uncommon, especially if replenished with bulky organic matter. Sandy soils tend to have low reserves and so too have several organic soils from which trace elements have been leached. In horticulture simple deficiencies of trace elements are mainly associated with growing in soil-less composts which require...
Sowing and aftercare in protected environments
The ideal conditions for raising plants from seed can be achieved in a protected environment such as a glasshouse or cheaper alternatives such as polythene tunnels or cold frames see p16 . Most seeds grown in protected culture are sown into containers see Figure 12.2 Figure 12.2 Range of containers for growing plants a traditional clay pots b standard seed tray and half tray c standard plastic pots in range of sizes, compared with d 'long toms' and e half pots f biodegradable pots g compressed...
Mineral uptake
Minerals are absorbed to form the soil solution see Chapter 21 . The plants take up only water-soluble material so all supplies of nutrients including fertilizers and manures must be in the form of ions charged particles . The movement of the elements in the form of ions occurs in the direction of root cells containing a higher mineral concentration Figure 9.4 Cross-section of Zea mais root showing its structure in the absorption and transport of water and minerals Figure 9.4 Cross-section of...
Soil development
The nature of a new soil regosols is largely determined by the rock minerals from which it is formed, but it continues to undergo changes under the influence of climate, vegetation, topography and drainage. These interact over time to give rise to characteristic soil profiles in different parts of the world. The soils that develop can be described in terms of the characteristics of the different horizons layers that make up the soil profile. The 'O' or 'L' horizon is the organic matter found on...
Other beetle pests
Springtime attack of flea beetle Phyllotreta species on leaves of young cruciferous plants e.g. cabbages and stocks is a serious problem to amateur and professional horticulturist alike see Figure 14.21 . In recent years, four other increasingly common beetle problems have been reported. These are viburnum beetle on Viburnum opulus, V. tinus and V. lantana, rosemary leaf beetle Chrysolina americana on lavender, rosemary and thyme, red lily beetle Lilioceris lilii on lilies, and asparagus beetle...
Alternatives to peat
Whilst peat remains a popular choice as a compost ingredient, great efforts are being made to find alternatives in order to preserve the wetland habitats where peat is harvested. A list of some of the materials used is given in Table 22.1. Much progress has been made by using suitably processed bark or coconut fibre in composts. Along with several other organic sources they are waste-based and recycling them helps in conserving resources. All such alternatives must be free of toxics and...
Migratory plant nematodes
The species of nematodes described above spend most of their life cycle inside plant tissues endoparasites . Some species, however, feed only from the outside of the root ectoparasites . The dagger nematodes e.g. Xiphinema diversicaudatum and needle nematodes e.g. Longidorus elongatus , which reach lengths of 0.4 and 1.0 cm respectively, attack the young roots of crops such as rose, raspberry and strawberry, and cause stunted growth. In addition, these species transmit the important viruses,...
Hydroponics Clay Balls
Sands are gritty to the touch even fine sand has an abrasive feel. Sand is mainly composed of quartz. Although any particle of this size is a sand grain, it is most often quartz because, unlike other minerals, it resists weathering. The shape of the particles varies from the rough and angular sand to more weathered, rounded grains. They are frequently coated with iron oxides, giving sand colours from very pale yellow to rich, rusty brown. Silver sand has no iron oxide covering. Chemically most...
Artificial control offlowering
A long night may be broken artificially using a technique called night-break lighting. Incandescent tungsten bulbs produce a high proportion of red light and are cheap to run. Hung about 1 m above the crop and spaced to give about 150 lux for four hours ensures that the Pfr730 critical level is not reached. Cyclic lighting saves electricity and uses a series of brief alternating light and dark cycles to replace one continuous break. High pressure sodium lamps are used where they are installed...
Compost mixing
It is most important when making up the desired compost formulation to achieve a uniform product and, commercially, it must be undertaken with a minimum labour input. The ingredients of the compost must be as near as possible to the specification for the chosen formulation. Materials must not be too moist when mixing because it then becomes impossible to achieve an even distribution of nutrients. There are several designs of compost mixer. Continuous mixers are usually employed by specialist...
Angiosperms and gymnosperms
The subdivision into class brings about the gymnospermae, mostly consisting of trees and shrubs, and the angiospermae representing the greatest diversity of plants with adaptations for the majority of habitats. Structurally, the gymnosperms have much simpler xylem vessels than the more complex system in the angiosperms, and flowers are unisexual producing naked seeds. The angiosperms usually have hermaphrodite flowers, which produce complex seeds see p103 , inside a protective fruit. Conifers...
Vine weevil Otiorhyncus sulcatus
This species belongs to the beetle group but, as with all weevils, possesses a longer snout on their heads than other beetles. Damage. The larva stage is the most damaging, eating away roots of crops such as cyclamen and begonias in greenhouses, primulas, strawberries, young conifers and vines outdoors, causing above-ground symptoms similar to root diseases such as vascular wilt. Close inspection of the plant's root zone will, however, quickly show the unmistakable white grubs see Figure 14.18...
Toxicity aspects of pesticides
The basic biochemical similarities between all groups of plants and animals means that any potential chemical chosen for its action against a weed, pest or disease may also be toxic to humans, pets, horticultural species and wildlife animals and plants. Prospective pesticides therefore have to go through a thorough examination over a period of several years to determine whether there are any dangers. This is carried out by the chemical companies and by contracted independent organizations. The...
The fruiting plant
The development of the true fruit involves either the expansion of the ovary into a juicy succulent structure, or the tissues becoming hard and dry. In false fruits other parts, such as the inflorescence, e.g. pineapple and mulberry, and the receptacle, as in apple, become part of the structure The succulent fruits are often eaten by animals, which help seed dispersal, and may also bring about chemical changes to break dormancy mechanisms see p151 . Some fruits described as being dehiscent ,...
Damping off Pythium and Phytophthoraspecies
These two fungi belong to the Zygomycota. Damage. These two similar genera of fungi cause considerable losses to the delicate seedling stage. The infection may occur below the soil surface, but most commonly the emerging seedling plumule is infected at the soil surface, causing it to topple see Figure 15.13 . Occasionally the roots of mature plants, e.g. cucumbers, are infected, turn brown and soggy, and the plants die. Rose plants often have high levels of Pythium around their roots as they...
Resistance to pesticides
The development of resistant individuals from the millions of susceptible weeds, pests and diseases occurs most rapidly when exposure to a particular chemical is continuous or when a pesticide acts against only one body process of the organism. Resistance, e.g. in powdery mildews, to one member, e.g. carbendazin, of a chemical group confers resistance to other chemicals in the same benzimidazole group. Growers should therefore follow the strategy of alternating between different groups and not...
Pollination
The flower's function is to bring about sexual reproduction the production of offspring following the fusion of male and female nuclei . The male and female nuclei are contained within the pollen grain and ovule respectively and pollination is the transfer process. Cross-pollination ensures that variation is introduced into new generations of offspring. Self pollination occurs when pollen comes from the same flower or a different flower on the same plant as the ovule, common in Fabaceae bean...
Chemical sterilization
This involves the use of substances toxic to most living organisms and must be used only by specialist operators and professional horticulturists. The chemical's toxicity to plants also means that they can only be applied to soil or compost that has no crops. With the recent discontinuation of methyl bromide, two remaining soil applied ingredients are dazomet applied outdoors and in protected crops as a granule against soil-borne insects, fungi, and weed seeds chemical substance intended to...
Annual weeds
While there are at least 50 successful annual weed species in horticulture, this book can cover only a few examples that illustrate the main points of life cycles and control. Two species, annual meadow grass and speedwell, are described. Annual meadow grass Poa annua . Plant family - Poaceae Graminae Damage. This species is a quite small annual or short-term perennial found on a range of ornamental and sports grass surfaces, on paths and in vegetable plots see Figure 13.8 . It is able to...
Food chains
Charles Darwin is said to have told a story about a village with a large number of old ladies. This village produced higher yields of hay than the nearby villages. Darwin reasoned that the old ladies kept more cats than other people and that these cats caught more field mice which were important predators of wild bees. Since these bees were essential for the pollination of red clover and clover improved the yield of hay , Darwin concluded that food chains were the answer to the superior hay...
Club root Plasmodiophora brassicae
This fungus is classified into a quite separate group of fungi, the Plasmodiophorales. Damage. It causes serious damage to most members of the Cruciferae family, which includes cabbage, cauliflowers, Brussels sprouts, stocks and Alyssum. Infected plants show signs of wilting and yellowing of older leaves, and often severe stunting. On examination, the roots appear stubby and swollen see Figure 15.12 , and may show a wet rot. Life cycle and spread. The club root organism survives in the soil for...
Artificial drainage
The low permeability of many subsoils, which create a perched water table, is the major reason for artificial drainage in horticultural soils. Clay, clay loam and silty clays, when wetted, become almost impermeable as the clay swells and the cracks close clay is 'puddled' to form a liner for ponds. This 'top water problem' is dealt with by putting in pipes to intercept the trapped gravitational water. Straight lines of pipes are placed at an even gradient from the highest point to the outfall...
Requirements for photosynthesis
In order that a plant may build up organic compounds such as sugars, it must have a supply of carbon which is readily available. Carbon dioxide is present in the air in concentrations of 330 ppm parts per million or 0.03 per cent, and can diffuse into the leaf through the stomata. Carbon dioxide gas moves ten thousand times faster in air than it would in solution through the roots. The amount of carbon dioxide in the air immediately surrounding the plant can fall when planting is very dense, or...
Inheritance of characteristics
As mentioned above, genetic information is passed from parent to offspring when material from male and female parent comes together by fusion of the sex cells. Genes from each parent can, in combination, produce an intermediate form, a mixture of the parents' characteristics in the offspring e.g. a gene for red flowers inherited from the male parent, combined with a gene for white flowers from the female parent, could produce pink-flowered offspring, if both conditions are equal see below . If...
Climate of the British Isles
The British Isles has a maritime climate, characterized by mild winters and relatively cool summers, which is a consequence of its proximity to the sea. This is because water has a much larger heat capacity than materials making up the land. As a consequence, it takes more heat energy to raise the temperature of water one degree, and there is more heat energy to give up when the water cools by one degree, when compared with rock and soil. Consequently bodies of water warm up and cool down more...
Chrysanthemum leaf miner Phytomyza syngenesiae
Damage. The leaf miners are a group of small flies, the larvae of which can do serious damage to horticultural crops by tunnelling through the leaf. This species is found on members of the plant family Asteraceae. Plants attacked include chrysanthemum, cineraria and lettuce. Life cycle. The flies emerge at any time of the year in greenhouses, but normally only between July and October outdoors. These adults, which measure about 2 mm in length and are grey-black with yellow underparts, fly...
Exotic predators and parasites
Figure 16.7 Glasshouse red spider mite predator. a Phytoseiulus predator eating glasshouse red spider mite b Eggs and young of Phytoseiulus c Application of Phytoseiulus to crop Figure 16.7 Glasshouse red spider mite predator. a Phytoseiulus predator eating glasshouse red spider mite b Eggs and young of Phytoseiulus c Application of Phytoseiulus to crop In greenhouses and polythene tunnels, high temperatures often all year round and sub-tropical species of plants bring with them exotic pests...
Types of inflorescence
The organs of sexual reproduction in the flowering plant division are flowers, and variation in their arrangement can be identified and named spike is an individual, unstalked series of flowers on a single flower stalk, e.g. Verbascum raceme consists of individual stalked flowers, the stalks all the same length again spaced out on a single undivided main flower stalk, e.g. foxglove see Figure 7.3 , hyacinth, lupin, wallflower compound racemes have a number of simple racemes arranged in sequence...
Peachpotato aphid Myzus persicae
This and similar species are often referred to by the name 'greenfly' Figure 14.8 . Damage. It is common in market gardens and greenhouses. The nymph and adult of this aphid may cause three types of damage. Using its sucking stylet, it may inject a digestive juice into the plant phloem, which in young organs may cause severe distortion. Having sucked up sugary phloem contents, the aphid excretes a sticky substance called honey-dew, which may block up leaf stomata and reduce photosynthesis,...
Stages Of Soil Formation
Erosion is the movement of rock fragments and soil. Erosion is the movement of rock fragments and soil. Figure 17.3 Rocks. Granite pink left silver top sandstone right slate bottom Figure 17.3 Rocks. Granite pink left silver top sandstone right slate bottom Igneous rocks are those formed from the molten material of the Earth's crust. All other rock types, as well as soil, are ultimately derived from them. When examined closely, most igneous rocks can be seen to be a mixture of crystals. Granite...
Glasshouse red spider mite Tetranychus urticae and T cinnabarinus
Damage. The piercing mouthparts of the mites inject poisonous secretions which cause localized death of leaf mesophyll cells. This results in a fine mottling symptom on the leaf see Figure 14.1 , not to be confused with the larger spots caused by thrips. In large numbers the mites can kill off leaves and eventually whole plants. Fine silk strands are produced in severe infestations, appearing as 'ropes' see Figure 14.25 on which the mites move down the plant. On flowering crops such as...
The naming of cultivated plants
The name given to a plant species is very important. It is the key to identification in the field or garden, and also an international form of identity, which can lead to much information from books and the Internet. The common names which we use for plants, such as potato and lettuce, are, of course, acceptable in English, but are not universally used. A scientific method of naming can also provide more information about a species, such as its relationship with other species. Linnaeus, working...
Methods of applying water
These should be carefully related to plant requirements, climate and soil type. On a small scale, watering cans or hoses fitted with trigger lances can be used, but care should be taken to avoid damaging the structure of the growing medium. Water can be sprayed from fixed or mobile equipment, but it is essential that the rate of application is related to soil infiltration rate The droplet size in the spray should not be large enough to damage the surface structure see tilth . Indoors, spray...
Field capacity FC
As gravitational water sometimes referred to as 'excess water' is removed, air returns in its place. On sandy soils this may take a matter of hours after the rain has stopped, but may take far longer on clay where the process may continue for many days. The soil is then said to be at field capacity FC . More precisely, it is a soil that has been saturated, then allowed to drain freely without evaporation until drainage effectively ceases. In practice it is assessed after two days. At field...
Stem growth
Apical meristem Protoderm Ground meristem Procambium Figure 6.6 The tip of a dicotyledonous stem showing the four meristematic areas Apical meristem Protoderm Ground meristem Procambium Figure 6.6 The tip of a dicotyledonous stem showing the four meristematic areas Growth of stems is initiated in the apical, or terminal, bud at the end of the stem the apex . Deep inside the apical bud is a tiny mass of small, delicate jelly-like cells, each with a conspicuous nucleus but no cell vacuole. This...
Leopard moth Zeuzera pyrina
Damage. The caterpillar of this species tunnels into the branches and trunk of a wide range of tree species, such as apple, ash, birch, and lilac. The tunnelling may weaken the branches of trees which in high winds commonly break. Life cycle. The Leopard moth has an unusual life cycle. The moth is large, 5-6 cm across, and is white with black spots. In early summer the female lays dark-yellow eggs on the bark of the tree. The emerging caterpillar see Figure 14.14 enters the stem by a bud, and...
Tissue culture
Tissue culture is a method used for vegetative propagation based on the phenomenon that any part of a plant from a single cell to a whole apical meristem can grow into a whole plant see totipotency . The explant, the piece of the plant taken, is grown in a sterile artificial medium that supplies all vitamins, mineral and organic nutrients. The medium and explant are enclosed in a sterile jar or tube and subjected to precisely controlled environmental conditions. This method has advantages over...
Conifer root rot Phytophthora cinnamomi
This fungus belongs to the Zygomycota group of fungi. Damage. This soil-inhabiting fungus is most commonly a problem in nursery stock production nurseries. It causes the foliage of plants to turn grey-green, then brown and eventually to die off completely see Figure 15.14 . Sliced roots show a chestnut brown rot, with a clear line between infected and non-infected tissues. Two hundred plant species, including Chaemaecyparis, Erica and Rhododendron species may be badly attacked. Figure 15.14...
Nutrient film technique NFT
This is a method of growing plants in a shallow stream of nutrient solution continuously circulated along plastic troughs or gullies. The method is commercially possible because of the development of relatively cheap non-phytotoxic plastics to form the troughs, pipes and tanks see Figure 22.5 . There is no solid rooting medium and a mat of roots develops in the nutrient solution and in the moist atmosphere above it. Nutrient solution is lifted by a pump to feed the gullies directly or via a...
Insect pests
Belonging to the large group of Arthropods, which include also the woodlice, mites, millipedes and symphilids see Table 14.1 , insects are horticulturally the most important arthropod group, both as pests, and also as beneficial soil animals. The body of the adult insect is made up of segments, and is divided into three main parts the head, thorax and abdomen see Figure 14.4 . The head bears three pairs of moving mouthparts. The first, the mandibles in insects such as in caterpillars and...
Flower structure
The flower structure is shown in Figure 7.4. The flower is initially protected inside a flower bud by the calyx or ring of sepals, which are often green and can therefore photosynthesize. The development of the flower parts requires large energy expenditure by the Stigma Style Ovary Ovule Sepal calyx Receptacle Pedicel Stigma Style Ovary Ovule Sepal calyx Receptacle Pedicel Figure 7.4 Flower structure, e.g. a flower of Glaucium corniculatumand b diagram of typical flower to show structures...
