Layerage

Stems that form root while still attached to the parent plant are called layers, and the practice based on this phenomenon is known as layerage. In some plants artificial methods must be employed, while in others root formation occurs naturally . the rooting medium is usually soil although other materials are used.

Uses:
Layerage is a rather certain method of inducing rooting.Some plants that cannot be started satisfactorily from cuttings can be grown with relative ease from layers, A cutting, having been severed from the plant on which it grew often does not remain alive until roots are formed. A layer, on the contrary, is supported by the parent plant indefinitely and, in the meantime, it is likely to develop rots.


Many plants produce natural layers freely and thus provide a ready source of new plants. This is true of the raspberry and strawberry and certain forms of the blackberry and dewberry. In these plants the layers are produced by either runners or upright canes that, by arching, come in contact with the ground and develop roots. Other plants produce natural layers form the crown of the plant. The quince and chrysanthemum illustrate this behavior.
On a small scale, layerage may be used to good advantage, for the reason that layers don not requirethe close attention as to watering, humidity, and temperature that cutting require Roses are sometimes grown from layers for this reason.
Objections to layerage are that it is a slow and cumbersome method of propagation; that is may interfere with cultivation; and that parents plants produce a limited number of new plants, so that a great number of stock plants must be provided .Despite these disadvantages layerage is used quite commonly in the propagation of some plants, an certainly has wide range of adaptation for the amateur gardener.

Simple Layers :
Branches that have formed roots in one aresa only are called simple layers. Such layers are made by bending the branches to the ground and covering the portion just below the tip with 3 to 6 inches to soil. This practice is usually carried on in early spring, before growth has started. The tip of the shoot is left exposed, to form lwaves and carry on the normal processes of the plant.
It is ac common practice to injure tho portion to be covered, by notching, cutting, girdling, or twisting. This practice destroys the phloem tissue, partially or completely, and retards the downward movement of foood matereals manufactured by the leaves of the exposed terminal potion., The result is an accumulation of plant food above the injured area, and such plant food is favorable to the development of roots by the layer. It is also considred that the injury checks the downward movement of hormones, and the concentration of these in the injured area stimulates Root Formation.
The season of the year for making layers varies with the species.With some the best results are obtained if layers are made in late winter or early spring; with others, late summer and fall seem to be transplanted successfully to a new lactation other require two seasons to develop a strong root system a strong root system.
Many different kinds of plants can be3 grown from simple layers. In actual use, however the method is restricted largely to very difficult species, and to plants grown for home use.
Tip Layers: A tip layer differs from a simple layer in that the tip is completely covered. Tip layers are used extensively in the propagation of some varieties of blackberries, dewberries and raspberries. In starring new plants by this method the tips of branches are placed int he soil, pointing downward, to a depth of 2 to 3 inches, and covered the soil is paced lightly to hold the branch securely in place. For the production of a larger number of plants a shallow furrow many be plowed along the row a short distance form the plants, and all the available lateral tips laid in the furrow and covered. Tip layers of berries are best made in late summer. The covered portion will shortly become etiolated and fleshy. Attentive roots will develop in from 2 to 3 weeks, and the layer can then be dug, severed from the parent plant , and replanted in ta permanent lactation. This can be done shortly after rotting occurs, but best results are obtained by allowing them to remain in place utile the following spring, and replanting at that time. The rooted layer should be replanted with tip pointing upward since the stem will develop from the terminal bud

Compound Layers.
Long shoots that are alternately covered and exposed over their entire length are known as compound layers.They normally form roots at each node where they are covered and develop new shoots from buds at nodes that are not covered . When they have grown one season or more, the several layers are severed so as to provide a root system on the proximal portion of each layer and a top on the distal portion. The time of the year for making and for replanting compound layers is influenced by several factors. Normally they are made in late winter and early spring. The rooted layers may occasionally be replanted later in the same season, but mere commonly they are allowed to grow one or two full seasons in order to develop a strong root system. Compound layerge is adapted to the prorogation of the Muscadine grape. The natural production of rosettes and roots by the strawberry plant at each second node o the runners is similar to compound layerage.

Trench or Continuous Lyares :
The type of layer differs from the compound layer in that the branch is covered for its enter length instead of alternately. This method in adapted to the propagation of own-rooted apple, pear, cherry, and other plants needed for research investigations or Therese . It can also be used on Muscadine and other kinds of grapes that do not root well from cuttings. Essentially, trench layerge consists of placing the main stem of a plant in trench in a way that will permit young stems to develop from later buds and to form roots on the lower portions of these new stems.Plants that produce long vines can easily be bent to the ground.Other like apple and pear, must be planted in horizontal potion with the roots in proper contact with the soil and the main stem in the trench. Obviously, this would be practicable only with small whip like plants. In practice three methods are used in covering continuous layers. By one method, the layer is planed in an open trench. New shoot develop from lateral buds, and when they are about 6 inches high, soil is added to a depth of avout 5 inches. Roots develop on the bases ot the shoot that are covered with soil. By another practice, about 1 inch of fine soil is added when the layer is first placed in the trench. The new shoots push upward through this layer. As the shoots elongate, more soil is added around them until they are covered to a depth of 5 to 6 inches. The bases of shoots that develop when treated in this manner are etiolated, a condition favorable to ready rot formation. By still a third practice, the layer is covered root to a depth of about 3 inches with loose soil when it is made. The shoots push upward through this layer and develop roots from the etiolated portion of the stem below ground.In every case, the roots arise adventitiously from the cambium layer of the new stems. The best
season for making contentious layers is in late winter or early spring. The rooted plants are allowed to develop one full growing season before they are removed from the parent layer and replanted.

Mound or Stool Layers :
This method is especially satisfactory for the rooting of apple and quince rootstock and issue in preference to interlayering when possible, as it involves less trouble and expense. A stock bed is established by setting young plants 3feet apart in rows 4 feet apart. The plants are headed back before growth starts and are allowed to arrow for one season. The following winter the plants are cut back within 3 inches of the ground leave, with the result that many new shoots arise from the base during the following season.In the case of appl;es, which root freely from these new shoots, the stools are allowed to remain uncovered during the early part of the growing season. The greatest number of shoots are produced in this way after they are formed and have reached the height of 8 inches thy re mounded with 5 to 6 inches of soil. Mounding should be done with moist soil, which should be planed from the center outward in order to bend the shoots out and give them better scarping. This spacing seems to give a better rooting especially with vigorous shoots.

When plums are being grown, the procedure is modified and the plants mounded before the new shoots rapper. This practice results in the formation of fewer new shoots than the other method, but the shoots that are produced are etiolated and form roots better than those that are produced before mounding. This applies not only to shoots from stools and layers but also to stems used for cuttings, from which better rooting is obtained when there bases have been etiolated during growth.

After the plants have been mounded by either method in early spring, they are allowed to grow during the rest of the season and roots will form on the new shoots along the covered portions of the stems. In early winter the rooted shoots are removed and planted in the nursery row .These parental set at a depth ao about 6 inches. They will be ready to bud during the summer of the following year, or they may be grafted at the end of one season in the nursery. The chrysanthemum forms natural mound layers from the overwintering crown at the beginning of each new growing season. These develop into new plants when thy are detached and planted out separately. Quince and Japanese flowering quince ave habits of growth that permit them to be propagated from natural layers from the crown of the plants. Varieties of currants and gooseberries that do not grow readily from cuttings are frequently grown from mound layers.

Air Layers.
A method used to root branches of upright growing plants that don not sprout or sucker readily is known as air layerage. Chinese layerage and pot layerge are other names for the same method.The stem is first injured by sliching, notching, rigging , or binding. Care must be exercised not to injure it sufficiently as to cause breadage or death of the layer. This can be effected easily by binding with copper wire wrapped tightly about the stem, and it has the same effect on rooting as the other treatments. It is common practice to apply a coating of one of the concentrated hormone dusts to the area where roots are to from.

Tissu Culture

Today, it is generally accepted that the term 'plant tissue culture' broadly refers to the cultivation in vitriol of all plant parts, whether a single cell, a tissue or an organ, under aseptic condition; although street has recommended a more restricted use of the term (20). Plant tissue culture is a technique which has great potential as a means of tentatively propagating economically important species; a potential which is being realized commercially at present. However, a tissue culture system is also very often a 'model' system which allows one to investigate physiological, biochemical, genetic and structural problems related  to plants and the technique is being used also as an adjunct to more traditional means in plant modification. Many of these approaches being used at present are described in succeeding chapters in this book. It is mainly in view of using tissue culture as a tool in basic and applied research that the requirements of a plant tissue culture facility will be examined in this chapter. 

The underlying principles involved in plant tissue culture are very simple. Firstly, it is necessary to isolate isolate a plant part form the intact plant and its inter-organ, inter-tissue and inter-cellular relationships. Secondly, it is necessary to provide the plant part with an appropriate environment  in which it can express its intrinsic or induced potential. This means that a suitable culture medium and proper culture conditions must be provided. Finally, the above must be carried out aseptically. In practice, this means that the culture must be free of bacterial, algal, fungal and other contaminants.Contamination by such microorganisms is a very peal problem in tissue culture and one which demands a great deal of skill, care and organization because the media used to support higher plant cell growth also supports the growth of these microorganisms. If their growth is not prevented, they may overgrow the plant cells, inhibit there development and interfere with the physiology and biochemistry of the system by the release of metabolic products. Secondly, we will see that much of the equipment used in a tissue culture laboratory is aimed at careful control of all the components pertaining to the physical (and to some extent as a consequence, to the physiological) environment of the system (e.g.media components, gaseous atmosphere, types of vessels used, light and temperature regimes, etc .) All this is aimed at ensuring that the system is as defined as possible. Nonetheless, It is important to realize the as De Sanford has pointed  out, it is very rare for any of us to attain optimal,fully defined, reproducible culture condition. No doubt a rational yet imaginative use of laboratory equipment coupled with a knowledge of which factors man or may not influence the system and how, plays an essential role toward achieving this somewhat elusive goal.The following topics are covered in this chapter: basic organization and facilities, glassware, instrument and miscellaneous equipment, controlled environments and liquid cultures.

Basic organization and facilities :

The cultivation of a plant tissue in vitro does not per require complex or expensive equipment. It has been said that all one really requires is a pressure cooker and few jam jars! The extent to which more sophisticated apparatuses are necessary depends on the nature of the research undertaken.For example, one may wish to investigate the ultra structural changes occurring in the course of the growth and different ion of a particular system. In that case an electron microscope and darkroom facilities will be required. Radiochemical student carried out on a tissue culture model system may necessitate the acquisition's of a high-speed centrifuge, a spectrophotometer, a freeze-dryer, etc. such requirements will not be reviewed here.

The basic organization and facilities of most tissue culture laboratories today can be summarized as follows.

Facilities

*** A general laboratory area with provisions for either Independent or common working spaces or both.      Some equipment and materials will necessarily be communal and should be easily accessible to all workers.

*** Large sinks (some lead-lined to resist acids and alkali) and draining areas. Washing machines to wash glassware in bulk and hot-air cabinets or ovens for drying washed glassware are useful in most cases.

*** Cabinet and shelf space for safe storage of chemical and dust-free storage space for clean glassware.

*** Transfer areas for aseptic manipulations. Such a facility can be provided in several ways and will   bee reviewed later.

*** An autoclave and / or oven for sterilizing media, solutions, water, culture vessels and instruments.

*** Culture rooms or incubators where cultures can incubated under controlled light, temperature, and if    possible, humidity  regimes.

Discripation

There are two sources of flooding in Bangladesh during monsoon. Water deposited in the upper watershed outside Bangladesh is brought by the rivers and we have upper-big or small-in the country. This destroys the standing crops, but it also brings silt and nutrients to the soil. The second source of flooding is rainfall within Bangladesh. The water the rain water and the water coming from outside is not a problem by itself. The big problem is how fast this water can be drained off the land. To solve this problem, our people have, over the centuries, dug thousands of canals and built thousands of embankments. These canals must be re excavated and these embankments reconstructed every few years during the dry season.

Normally, cover of some kind are used for cold frames and hotbeds. The most satisfactory cover is the standard sash. It 3 ft feet wide and 6 feet long. Glass panes are imbedded in the frame and glazed to provide waterproof and airtight protection. In use the sash is placed lengthwise across the cold frame or hotbed. The standard sash is expensive; yet it is a satisfactory cover. A frame cover with glass permits the absorption of heat from the sun on clear days. And it enables the bed to retain it during the night and during cold period; it is possible in this way to provide temperature that are more uniformly favorable for plant growth than would be the case if the frames were not so covered. Various other materials are used as covers for cold frames. Screen wire imbedded in a transparent material similar to cellophane makes a satisfactory cover. This material is usually tacked on frames of dimensions that perm it of convenient handling. Different grades and weight of cloth that range from heavy duck to light domestic are also used. The untreated cloth may be used, but treating the material with hot linseed oil or melted paraffin increases its durability, makes it more nearly waterproof and airtight, and renders it more effective in protecting the frame during unfavorable weather.


Methods of Heating Hotbeds. Heating of hotbeds is accomplished in four principle ways


Hot water or steam.

Where hotbeds adjoin a greenhouse that is heated by steam or hot water, the heating pipes may be extended in to the beds also. Other provisions are sometimes made for steam or hot water. The pipes are usually placed about 5 or 6 ins below the seedbed surface. Where it is desired to protect plants against an occasional late frost or freeze, and where it is desirable to warm the air, but not necessary to warm the soil, the pipes may be suspended along the inside walls at about the level of the seabed. Hotbeds heated with steam or hot water is very satisfactory because the temperature can be regulated accurately.


Organic Matter

The heat liberated in the decomposition of organic matter can be used as a source of heat for hotbeds. Animal manures are used commonly and fresh manure from grain-fed horses is considered best. Hay, straw, and cornstalks are also used, thought the heat produced by these is much less. The hotbed is excavated to a depth of from 18 to 30 inches. The manure or other organic material is packed well into this basin, especially around the edges and in the corners. When the required amount has been added, a layer of good soil, 4 to 6 inches deep, is spread smoothly over the top. This constitutes the seedbed and its surface should be slightly higher than the level of the surrounding ground. When moisture is added, heat is produced by organic material and the seedbed above absorbs some of the heat. The greatest heating effect is at the beginning of the period, and the temperature gradually subsides. Hence, this type of hotbed is more satisfactory for use in the spring than in the fall. If manure, or other organic material, is available locally, the chief expense of providing heat is the labor necessary to put the bed in operation


Flue Heat

By another method, hotbeds are heated by flues. In the construction of such beds, a firebox lengthwise of the bed to an outlet at the opposite end. Two lines of flues, properly spaced, give a more uniform distribution of heat than if only one line is used. Soil is placed over the flues to provide the planting bed. Hot gas and smoke from the firebox, passing under the bed, create the heating effect. Cheap fuel is essential for the practical operation of a flue-heated hotbed. Wood has been used more commonly than any other fuel, but high labor costs are making it more expensive. Careful and regular attention is required to provide uniform heat; hence the labor cost of operation is high. They are inconvenient to operate, particularly when it is necessary to provide heat day and night for a prolonged period.


Electricity

As electricity becomes more generally available, it is being used increasingly in the heating of hotbeds. Light bulbs, mounted on suitable panels, and suspended in the air within the hotbed, may be kept burring short to keep the air temperature above the danger point during short cold periods. Several low-watt-power globes distributed over the entire area to be heated are preferred to s smaller number of high-watt-power globes. In addition to the hearting effect, light bulbs provide supplemental light which is advantageous in some cases; Special lead- and plastic-cover heating cables are now available for heating hotbed soil. The cable is laid back and forth across the bed 4 to 6 inches deep over it. A thermostat may be used to control the temperature at which the electric current will cut off and on. The soil temperature to be provided varies with the different kinds of plants to be grown in the hotbed. For tomato and sweet potato the thermostat is set so that current will be cut off if the soil temperature rises above 85° F. and will come on again if the temperature drops below 75°F. When the cable has been installed with a thermostat, a favorable soil temperature is provided automatically and the labor cost for operation is reduced to a minimum. The amount of electricity required, and hence the4 cost for heating hotbeds, depends principally upon (1) the temperature required, (2) the amount of cold weather which prevails, and ( 3) the type of hotbed and covers used.

With sweet potatoes in Texas, 13 kilowatt-hours of electricity were required to produce 1000 plants when the bed was covered with standard sash, but 23 were required when a cloth covering was used. Beds banked with soil (as insulation) required 27 kilowatt hours for each 1,000 plants, while 51 were required for the beds without insulation. The plants were 5 days earlier in the beds covered with standard sash and in the insulated beds than in check cooler, For several locations in Texas the electricity for heat to produce sweetpotapo slips ranged from 1.7 kilowatthours per 1,000 plants ranged from 7 to 13 kilowatthours at different locations, depending upon the amount of cold weather the prevailed during the period of operation. Oftentimes costs are calculated upon the electricity required to provide heat for the area covered by one standard sash. Thus tests in Washington and Pennsylvania show that the cost during a certain period was almost 3 cent per sash are week; while under different conditions, in Maryland, the comparative cost was only about 1.5 cents per sash per week. very important in our country.

Horticulture

The plant is the basic source of all food and consequently the determining factor in life. The fundamental process of photosynthesis,by which the plant is able to combine water and carbon water and carbon dioxide to form sugar, permits the synthesis of the more complex compounds by the plant and the use of these compounds by man and the lower animal to sustain their life processes. From the earliest time, when herdsmen sought and processes. From the earliest times, when herdsmen sought and protected grass for their heard up to present period of diverse plant form, man has always had a fundamental interest in the production and care pf plants.

As soon as some adventurous soul found a fruit, a berry or a plant to be edible, it immediately became an object of solicitous attention. The best type were selected and propagated by any means available,

usually seeds, with the result that many new forms were constantly coming into being from which better selections could be made. Over a long period of years, this precess of selection and preparation of new and better types has resulted in an array of plant materials that is lavish beyond the imagination of earlier generation.

As man began to grow these plants in gardens, he became aware of the beauty that develops in any systematic and well-cared -for planting. He began to seek and select flowering plants, ornamental shrubs, and trees of all kinds and to blend them into pleasing landscapes. This later development of ornamental horticulture has expanded with ever-increasing enthusiasm. with all the magnificent of earlier gardens of both past and present, there is little reason to doubt that even greater achievements will be made in this field in the future.

The Structure of Plants

The propagation Culture and management of horticultural plants are based to a considerable extent upon a knowledge of the structure units of the plant, which are known as organs, are the roots, stems, laves, flowers, and fruits. Each is composed of several defer ant kinds of tissue, such as xylem, Phloem, and cambium, and this tissues, in turn, are composed of cells. Some cells have thick walls, others have thin walls; cells differ also in size, shape, and cell contents. The three principal types of cells in plants are parenchyma, and collenchymas.

Roots :

The roots are essential organs of most plants. The chief functions of roots are to absorb moisture and nutrients for the plant and to provide anchor for it. The following kinds of roots may be conveniently considered from the standpoint of origin, structure, and function

Primary roots :

The radical of a germinating seed produces the first foot of the new plant. This is the produces the first root of the new plant. This the primary root produces the so-called ‘taproot.’ In some plants, as walnut and hickory, the growth of the taproot  predominates for several years, and they are commonly regarded as tap rooted

Plants :

Secondary and Lateral Roots. Branch roots that arise from the taproot are known as secondary foots is horizontal. Roots that develop laterally on any previously fumed root roots are known as lateral roots. In reality, may develop from the taproot, from other lateral roots, or in some cases from stems. There is considerable variability in the extent of branching shown by roots of different species of plants. The tomato is an example of a plant in which free branching occurs; root branching in the onion, on the contrary occurs less freely; and the hyacinth produces roots that are normally unbranched.

The peach and apple are examples of plants is which there is limited development the taproots but extensive development of the lateral-rooted roots. Plants in which this occurs are known as lateral-rooted plants. The spread an depth of the root system and the extent of branching in poor soil. Hence plants in sandy soil of low fertility tend to produce long rots with relatively few branch roots.

As the radical of the germination seed begins to grow, it consists initially of primary cells which form primary tissues. As it and the branch roots that develop from it continue to grow, the region extending a short distance from the tips is characterized by primary growth. Branch roots arise from the epicycle tissue, at a postal ways shortly back of the growing tip. The youngest roots are always nearest the  tip of the root, and the older ones are toward the base. Since they thus develop in regular succession, they are known as regular or acropolis roots.

Adventist Roots :

Those that arise from other tissue and organs of the plant than the percycel of young roots are called varying degree of readiness, from toots, stems, leaves, and modified part of the principal kinds of horticultural plants They never, or rally, from the stems of certain onse; they form readily from the roots and stems of some dicotyledonous plants, but les readily from other; they form quite readily plants, but not from gymnosperms. The tissue from which adventives roots originate are principally the cambium, and callus of stems, and the parenchyma tissue near cambium of vascular bundles of leaves.

Root Hairs :

Simple, hair like outgrowths of the outer walls of cells of the epidermis of the root are produced by many plants. These are known as root hairs. They grow out into space between soil particles and absorb moisture and nutrients for the plant. Most of the higher vascular plants, such as peach, apple, grapefruit, cranberry, and pecan, do not have normal root hairs, at least under certain soil conditions. With these the absorption of moisture is performed by various small lateral roots. They function for a short time as absorbing organs; then they either die or begin secondary growth and become part of the permanent root  which consist of primary tissue, it is obvious that the root hairs occur only on the terminal portion of young growing roots. Root hairs normally function only during a relatively short period. As they wither and disappear, others develop near the terming growing point of the root.

Stem

In the germination of a seed the plumule produces the first stem of the new plant. The continued growth for one or more seasons of this first stem and, in most species, the branching of it produce the trunk and framework of the new plant. Stems, in turn, produce the buds, leaves, flowers, and fruit. They also serve as conducting systems for water and nutrients between the roots, leaves, and fruit. The principal groups of horticultural plants are angiosperms and gymnosperms.

Monocotyledonous Plants :

In general str4ucture the stem of these plants consist of a terminal growing point, nodes, buds, and internodes. In cross section the stem consists of epidermis, perhaps a cylinder of thick-walled schlerenchyma beneath the epidermis, and isolated vascular bundles distributed in a mass of fundamental tissue similar to the pith of dicotyledons. The internodes of monocotyledonous plants provide most of the length growth of the stem. The lower part of each internodes is region of elongation. This in part accounts for the exceedingly rapid length growth of stems of certain monocotyledonous  plants, such as the bamboo, Johnson grass, and asparagus.

The elongation of the stem many continue for many years. The date palm, for example, lives for an indefinite period and may ultimately grow to be 50 feet high, corm, on the country, survives only one season and rarely grows taller than 6 to 8 feet. In some species the terminal growing point produces the inflorescence of the plants. This is true of the onion, and also of corn, which produces the tassel terminally on the main stalk and the postulate inflorescence  on a lateral branch.

The nodes of monocotyledons sometimes give rise to auxiliary buds Such buds are rare on the date palm, with the result that the plants normally produce single entrenched stems with only occasional offshoots. Corn, on the contrary produces buds freely at the nodes, some of which grow into branch stems while others produce the ears of corn.

Dicotyledonous and Gymnosperm Plants :

Young stems of these plants have a pith, xylem, cambium, phloem, epicycle endodermis, cortex, and disappeared, and exposed phloem cells form a perineum, or bark. Stems of dicotyledons make terminal growth by elongation of cells near the tip of a growing branch. the terminal growing point in its process of growth may (1)  produce a terminal bud, from which growth will be4 resumed the following season,  (2)  produce a terminal inflorescence as in the gape, apple, pecan, walnut, cabbage, and carrot, or (3) it may about , in which case future growth of the stem will be from an axillary’s bud below.

Young in the process and development differentiate into nodes and inter nodes. Leaves and buds are normally formed at nodes. The area between nodes is known as the interned. The inter nodes in stems e very short, as in cabbage, or relatively long, as in the grape, depending on the species. Rapidity of growth caused by growing conditions also influences the length of the inter nodes of many species.

The cambium layer of stems of these plants is of peculiar interest and concern because of its relationship to several important horticulture practices and treatments. Briefly, the cambium layer serves the plant in these ways; (1) It is the systematic tissue responsible for increase in size of the stem after it begins secondary growth . Cambium cells occur in a continuous ring between the xylem and phloem. During each season of growth they enlarge and divide and differentiate into now xylem cells toward the inside and now phloem cells toward the side. If the cambium fails to function because of mechanical injury or physiological causes, no xylem and phloem are formed. Since these tissue are essential to the normal growth of a plant, death results if the activity of the cambium layer is restricted for a prolonged period. The healing of wounds is made possible by the cambium layer and is accomplished by two processes, Regeneration may take place where bark is removed and living cambium cells are exposed on the surface of the wood. Under the favorable conditions of high humidity and warm temperature such cells may become active and reconstruct new tissues on the surface of the wound. New growth from these cells is outward in a radial direction. Over walling takes place as a result of the growth in a lateral direction of cambium cells around the margins of a wound, causing now tissue to advance from various sides to cover the wound.(3) The cambium produces callus tissue which is essential to the success of budding and gifting. Callus also forms on the cut ends of cuttings of some plants. This may provide   protection against decay-producing organisms. In tare cases, roots arise directly from the callus tissue, though in most cases they arise directly from the callus tissue, though in most cases roots they arise directly from the callus tissue, though in most cases thy arise directly from the cambium and callus is not essential tooting. (4) Finally, when adventitious roots develop on stems or on contained cells near the cambium.

Buds

A bud is a growing point, surrounded by small, partially developed leaves. Its is in reality a rudimentary stem in a state of dormancy or limited growth, protected by an envelope of scales. It may consist of a mass of meristematic cells or of several nodes and very short internodes. Close examination of a well- developed bud reveals leaves and buds in the same order as on a growing stem of the same plant. Several classifications of buds origin, position on stem, position on node, time at which they begin growth, and function.

Position on Stem :

In the growth of buds are formed at different positions, The principal kinds of buds, with regard to their location on the stem, are terminal, auxiliary and lateral. Terminal buds are those that develop from the terminal growing point at the end of a stem when growth cusses. In some kinds of plants, they are formed regularly; in others the growing point tends to about, leaving no bud does form, it is usually the one to engine growth firsts the following spring. A terminal bud is regard as being dormant or largely so; whereas a terminal growing point is regarded as being in a state of active growth and elongation. An maxillary bud is one that occurs in the axil of a leaf- the angle between the leaf and the stem. They are designated as as axillary’s buds even after the leaf has shed. These buds are also properly calls lateral buds, however may occurs jor where the leaf was rudimentary. Examples of the latter class are frequently observed on parts of pecan shots that are formed near the end of the growing seasons. The peach, tung tree, and less frequently the rose produce shoots with certain nodes and leaf axils at which no buds occur, These are commonly blind buds or blind nodes.

In most species only a single bud develops in the axil of each leaf. In some, however, two , or even more may may develop, The bud nearest the terminal of the shoot is usually the largest of the group and is named the primary hub. Commonly, however, all except the primary bud are referred to collectively as the secondary, or reserve, buds. The p[remarry bud is the one of the group most likely to grow when the tree starts growth in the spring. The reserve buds oftentimes begin normal growth with the primary buds, but they are especially likely to grow under conditions of excessive soil moisture or if the growth from the primary bud is injured by cold weather, insects, or other causes.

Vegetative and Flower Buds.

The growth in height of a plant and the production of branches is due to the growth of vegetative buds. These are also called leaf buds.

Flower buds contain the rudimentary blossoms with various parts of the flower enclosed. Since flowers normally produce fruit as they continue to grow and develop, these buds are also known as fruit buds,. Flower buds develop from, of in close association with vegetative buds ;  hence, they occur on plants in the same general position as vegetative buds. In others, the two are quite similar in appearance.  The formation of flower buds takes place in some species during the season pro virus to the own in which the flowers appear. In other species the flower buds do not form until a time shortly before the buds begin to grow. In the peach, for example, the flower buds that boom in the spring ate formed during the previous summer and fall. Flower buds of citrus develop in late winter or early spring preceding the blooming period. An accumulation  of stored food in a plant is regarded as favorable for fruit-bud formation, and this accounts for the considerable variation in the time within a species when flower buds are formed.

Some species of plants produce mixed buds. The contain both flowers and vegetative parts within the same bud; consequently, when they begin growth they prejudice both vegetative in the time within a species when they produce both vegetative growth and flowers. The apple, pear, and blackberry are plants that produce mixed buds.

Dormant and Latent Buds :

 The buds of most fruits develop and mature during a given season and remain dormant over winter. Such buds begin growth the following spring and either develop into shoots of fruits or fall off, or they may remain dormant for a period of one to several years, in which case they are called latent buds. They may even become covered over by layer of bark; however,these latent buds usually make sufficient annual growth outward to prevent them form being over walled. When trees are cut back heavily, any of the 'water sprouts' that develop arise from latent buds

Adventitious Buds :

Normally shoots arise from well- formed buds, but occasionally they develop from other tissues, which form adventitious buds and shoots that grow from these are called adventives. Those that arise from foots are known as ‘suckers’ form example buds of the pear, blackberry, and persimmon plants. The point  of their origin is in the cambium of roots. Adventives shoots may also arise from stems. These originate principally in the cambium layer. Those that occur on the body or framework of trees and which make rank, venous growth are called ‘water sprouts.’ Most such shoots, however, arise from latent buds. Adventive shoots, however, arise from latent buds. Adventive shoots are also produced readily by leaves of some plants and less readily by others. The shoots originate from parenchyma  tissue close to the vascular bundles in leaves of dicotyledonous plants; and frequently from callus, formed at the cut or injured portion of the leaves of monocotyledonous plants.

Leaves :

Mineral nutrients and water from the soil are combined with carbon dioxide in the leavers, under the influence so sunlight, to form plant foods essential to growth. Leaves are later appendages formed by the stem in elongation. Plants that shed their laves at certain seasons, and hence have a period during each yearly cycle when they are bare and another when they are in full foliage, are known as deciduous plant. Examples are peach and apple. Those that retain their leaves for long periods, and do not shed all of them at one time but shed them so gradually that the trees have leaves on them at every season of  the year, are known as evergreen plants. Broad-leaved every greens are represented by such plants as citrus and cherry laurel, which retain their leaves form more that on year, and by other such as the live oak and ya upon, which retain them only until new le3aves are formed the following spring. The pines, arborvitaes, spruces, and junipers are examples of the coniferous evergreens.

Some horticulture plants are grown primarily for their vegetative parts. Other are grown for the flowers, fruits, or seed which they produce.  

Inflorescence :

Al;though the flowers of many plants are borne singly on stalks or stems known as pedicels, in numerous other cases the flowers are cases the flowers are borne in clusters known as inflorescence. The principle parts of the inflorescence are the peduncle, pedicels, and individual flowers.

 The peduncle is the main stem or central axis. Form it arise the pedicabs or in many cases the flowers directly without pedicabs. A flower, then many be borne one a pedicel or it may be attached to the main axis pr peducle without any stalk or pedical, in which case it is known as sessile. The area of attachment of the flower to the pedicel, or in the absence of a pedicel, to the peduncle is known as the receptacle.There are several distinct types of inflorescence,such as spike, raceme, corymb head, fascicle, and glomerule, based upon the position an relationships of the different parts. A determinate inflorescence, for example, is one in which the inflorescence is on in which the terminal remains vegetative, with flowers borne laterally as in the cabbage and hyacinth. In some cases the peduncle is branched, giving rise to a compound inflorescence.In some flower clusters both simple and compound types are represented. this is true in the Grape and cabbage.t

Flowers :

The flower is the forerunner of the fruit and seed. In order to consider the proceed that result in fruit and seed formation, it is important to give some though of flowers. There are two essential parts of the stigma, the style, and the ovary, which is the lower, enlarged portion. In it are borne the ovules, which when mature, become seeds. The style forms the connection between the ovary and stigma, and through it the pollen tube passes on its way into the ovary. The stigma represents the upper portion of the pistil; its receives the pollen and affords a favorable medium for its germination.

Special equipment is used in the growing of many horticultural plant. This equipment is used to start plant at seasons when out side condition are unfavorable, to grow plants to maturity at off seasons of the year, and for the propagation, by maturity at off seasons of the  year, and for the propagation, by seed or vegetative methods, of plants that require special treatment.

Types of Special Equipment :

There are several  different types of kinds of special equipment. The kind or species of plant to be grown, the length of time the entrapment is needed during a season, initial cost, operating expenses, and other similar factors are considered in deciding upon equipment to be used. 

Forcing Hills and Plant Protectors :

Certain structures are designed to cover the  individual plants in the field. They are known as forcing hills or plant protectors.

Types :

Several types are used. Formerly, one made in the form of a box, usually 12 inches square and 12 inches high with a pane of glass for cover , was used extensively. The initial cost, cost of storage, breakage and labor required to place them over the plants and removed them have all tended to discourage their  use.

Other types of plant protectors, however, are used for growing plant in the open. Small conical cover made of translucent paper or plastic are used commonly. Some plastic cover are flexible and are designed for using once only others rigid and may be used reputedly.

Uses :

Plant protectors and forcing hills are used to protect plants form untimely cold weather and form damage by wind. They are also used to increase the soil temperature to a degree which is favorable for the germination of seed. Workers in Arkansas have shown that muskmelon seed planted early in the spring germinate quicker when plant protectors are used, be cause of the higher prevailing soil temperature. The plants which got an early start ultimately produced marketable melons at a slightly earlier date than plants in locations where no covers for crops that produce a heavy yield of a valuable product form an individual plant. The tomato and muskmelon are examples of such plants. On the contrary, it would be impracticable to use forcing hills for carrots or radishes because the unit return from an individual plant of such crops is too small to justify the expense for labor and material.

Cold Frames and Hotbeds :

Cold framers are designed primarily to protect plants from cold without the use of artificial heat. Hotbeds differ from cold framers in that they are provided with artificial heat.

Uses :

Cold frames and hotbeds are used widely in the starting of vegetable crops, and to a lesser extent for cuttings. Cold framers are used primarily in protecting plants against a few degrees of cold, usually in early spring. They are also useful in providing protection against wind and excessive rainfall, and in the hardening of plants prior to transplanting to the field, a practice that is discussed in the chapter on transplanting. In some places, crops are started in cold frames and, when the water permits, the frames are removed and the crops continue. Plants may be grown in hotbeds at seasons when it would be too cold for them in cold frames; Oftentimes, Young plants are started in late winter in a hotbed and later as the weather becomes milder they are transplanted to the cold frame. After a period of growth there, they are finally moved to the field when outside weather conditions have become favorable.

Construction :

Cold frames and hotbeds are constructed in the same general manner. They are usually made of wood or concrete. When wood is used, the structures can easily be made so that they are movable, This makes it possible to set them up at different places each year and to store them during off seasons. Insulating the walls, particularly those made of wood, makes them more effective in retaining heat and providing protection. This is cor manly done by lining inside walls with heavy paper or by banking soil against the outside of the walls. The standard width of cold frames and hotbeds is 6 feet; the length is variable, depending upon the space needed. Cold frames and hotbeds should be located on the south side of a building or other barrier which will provide protection from north winds. The lengthwise direction should be from east to west. The north wall of the structure should be 6 inches higher than the south wall. This facilitates shedding of water when the frame is covered. It provides better exposures to sunlight in late winter and early spring and also provides some protection form north winds. The bed or floor of the cold frame or hooded should be even with, of slightly above the surrounding ground level to ensure good drainage. When concrete is used to make a permanent structure, the wall usually extend well into the soil and therefore special provision should be made to provide adequate drainages by the use of a sand or  gravel fill and tile drains.

Classes of Plants

There are many different system of classifying plants, from the standpoint of botanical relationships and stage of development. As viewed by the horticulturist, however, plants may be classified c cording to the relative of time that they require to couplet a cycle of growth.

Life Cycle of Plants The life cycle of any plant is the entire process of growth that is involved from the germination of the seed to the predication of a crop of seed by the new plants. The actual duration of this period is very variable, since some plants mature and produce seed much more quickly than others. Portulaca and some of the graze finish the life cycle in a few weeks, while the Northern spy apple does not bear fruit and make seed until ten to fifteen years old.
The behavior of certain plants, from the standpoint of the life cycle, is quite different from that of other.One group of plants, known as mono clinic, produces only one crop of seed and then dies. in many of these plants the length of life many be prolonged by preventing them from flowering and producing seed. plants, which  may also be said to have completed their life cycle when they produce seed, do not die but continue to live  and produce seeds for many years.

Floriculture And Ornamental Horticulture

The commercial production of flowers and the production of tree and shrubs for landscape planting are much more recent developments, but both have reached tremendous proportion in a shout period  of time. There are at present approximately 6,00 major growers of floral craps and 12,000 others operating on a lesser scales, employing 160,000 people and utilization  210  million square feet of greenhouse space. The wholesale floriculture carp amounts to 3.5 billion and the retail business to 8.5 billion  The nurseries of the Unites State have a capital investment of 1 billion and average annual crop value of 99million.

Throughout the world, thee are many horticultural industries of outstanding interest and significance, such as the bulb industry of Holland, coffee in Brazil and Central America, bananas in Central and South American, and cacao in several of the tropical  areas, principally in Asia and Africa. In the case of cirrus world production, representing many counters, reached the staggering total of 500 million boxes in 2000-2011 

In connection with these major phases of production based on type of plant material involved, there are also several important kinds of work that involve various plants in each group. Propagation of plants is accomplished by many different methods, of which see dag is the  most common:  other methods include the use of various plants parts such as bulbs, rhizomes or tubers, layers or cutting, and finally budding and grafting. These practices are fundamental in the many types of greenhouse and nursery industries: and even in the case of seed age many new techniques are constantly being developed  to aid grows.

Precessing of horticulture products by dehydration, pickling, canning, and quick freezing represent another industry that has expanded rapidly in recent years. For example, the canned pack of  three vegetable and three fruits in a recent average season was 125 million cases. the pack of reopen vegetable was 990 million pounds:  of only three fruits, 300 million pounds: and of frozen citrus concentrates, 50 million gallons. Breeding of horticultural crops and testing of variates are other types of work which continue to be increasing importance from year to year.New materials are being continually introduced from other and new methods of inducing variations have resulted in a much wider range of characters for select. A few yer ago, most frut varieties were the result of chance seedling, but each year an increasing number of new varieties with desirable characters are being made available  as a direct result of this breeding program.

There are two sources of flooding in Bangladesh

There are two sources of flooding in Bangladesh during monsoon. Water deposited in the upper watershed outside Bangladesh is brought by the rivers and we have upper-big or small-in the country. This destroys the standing crops, but it also brings silt and  nutrients to the soil. The second source of flooding is rainfall within Bangladesh. The water the rain water and the water coming from outside is not a problem by itself. The big problem is how fast this water can be drained off the land. To solve this problem, our people have, over the centuries, dug thousands of canals and built thousands of embankments. These canals must be re excavated and these embankments reconstructed every few years during the dry season.

Normally, cover of some kind are used for cold frames and hotbeds. The most satisfactory cover is the standard sash. It 3 ft feet wide and 6 feet long. Glass panes are imbedded in the frame and glazed to provide waterproof and airtight protection. In use the sash is placed lengthwise across the cold frame or hotbed. The standard sash is expensive; yet it is a satisfactory cover. A frame cover with glass permits the absorption of heat from the sun on clear days. And it enables the bed to retain it during the night and during cold period; it is possible in this way to provide temperature that are more uniformly favorable for plant growth than would be the case if the frames were  not so covered. Various other materials are used as covers for cold frames. Screen wire imbedded in a transparent material similar to cellophane makes a satisfactory cover. This material is usually tacked on frames of dimensions that perm it of convenient handling. Different grades and weight of cloth that range from heavy duck to light domestic are also used. The untreated cloth may be used, but treating the material with hot linseed oil or melted paraffin increases its durability, makes it more nearly waterproof and airtight, and renders it more effective in protecting the frame during unfavorable weather.

Methods of  Heating Hotbeds. Heating of hotbeds is accomplished in four principle ways

Hot water or steam.

Where hotbeds adjoin a greenhouse that is heated by steam or hot water, the heating pipes may be extended in to the beds also. Other provisions are sometimes made for steam or hot water. The pipes are usually placed about 5 or  6 ins below the seedbed surface. Where it is desired to protect plants against an occasional late frost or freeze, and where it is desirable to warm the air, but not necessary to warm the soil, the pipes may be suspended along the inside walls at about  the level of the seabed. Hotbeds heated with steam or hot water is very satisfactory because the temperature can be regulated accurately.

Organic Matter :

The heat liberated in the decomposition of organic matter can be used as a source of heat for hotbeds. Animal manures are used commonly and fresh manure from grain-fed horses is considered best. Hay, straw, and cornstalks are also used, thought the heat produced by these is much less. The hotbed is excavated to a depth of from 18 to 30 inches. The manure or other organic material is packed well into this basin, especially around the edges and in the corners. When the required amount has been added, a layer of good soil, 4 to 6 inches deep, is spread smoothly over the top. This constitutes the seedbed and its surface should be slightly higher than the level of the surrounding ground. When moisture is added, heat is produced by organic material and the seedbed above absorbs some of the heat. The greatest heating effect is at the beginning of the period, and the temperature gradually subsides. Hence, this type of hotbed is more satisfactory for use in the spring than in  the fall. If manure, or other organic material, is available locally, the chief expense of providing heat is the labor necessary to put the bed in operation

Flue Heat :

By another method, hotbeds are heated by flues. In the construction of such beds, a firebox  lengthwise of the bed to an outlet at the opposite end. Two lines of flues, properly spaced, give a more uniform distribution of heat than if only one line is used. Soil is placed over the flues to provide the planting bed. Hot gas and smoke from the firebox, passing under the bed, create the heating effect. Cheap fuel is essential for the practical operation of a flue-heated hotbed. Wood has been used more commonly than any other fuel, but high labor costs are making it more expensive. Careful and regular attention is required to provide uniform heat; hence the labor cost of operation is high. They are inconvenient to operate, particularly   when it is  necessary to provide heat day and night for a prolonged period.

Electricity  :

As electricity becomes more generally available, it is being used increasingly in the heating of hotbeds. Light bulbs, mounted on suitable panels, and suspended in the air within the hotbed, may be kept burring short to keep the air temperature above the danger point during short cold periods. Several low-watt-power globes distributed over the entire area to be heated are preferred to s smaller number  of high-watt-power globes. In addition to the hearting effect, light bulbs provide supplemental light which is advantageous in some cases; Special lead- and plastic-cover heating cables are now available for heating hotbed soil. The cable is laid back and forth across the bed 4 to 6 inches deep over it. A thermostat may be used to control the temperature at which the electric current will cut off and on. The soil temperature to be provided varies with the different kinds of plants to be grown in the hotbed. For tomato and sweet potato the thermostat is set so that current will be cut off if the soil temperature rises above 85° F. and will come on again if the temperature drops below 75°F. When the cable has been installed with a thermostat, a favorable soil temperature is provided automatically and the labor cost for operation is reduced to a minimum. The amount of electricity required, and hence the4 cost for heating hotbeds, depends principally upon (1) the temperature required, (2) the amount of cold weather which prevails, and ( 3) the type of  hotbed and covers used.

With sweetpotatoes in Texas, 13 kilowatt-hours of electricity were  required to produce 1000 plants when the bed was covered with standard sash, but 23 were required when a cloth covering was used. Beds banked with soil (as insulation) required 27 kilowatthours for each 1,000 plants, while 51 were required for the beds without insulation. The plants were 5 days earlier in the beds covered with standard sash and in the insulated beds than in check cooler, For several locations in Texas the electricity for heat to produce sweetpotapo slips ranged from 1.7 kilowatthours per 1,000 plants ranged from 7 to 13 kilowatthours at different locations, depending upon the amount of cold weather the prevailed during the period of operation. Oftentimes costs are  calculated upon the electricity required to provide heat for the area covered by one standard sash. Thus tests in Washington and Pennsylvania show that the cost during a certain period was almost 3 cent per sash are week; while under different conditions, in Maryland, the comparative cost was only about 1.5 cents per sash per week. very important in our country.