Glossary
Plain-language definitions of the botanical and bonsai terms used across the courses, each linked to the lesson that teaches it.
The movement of a substance into or out of a cell against the direction it would drift on its own, which takes energy. Much of a root's mineral uptake works this way, powered by respiration, so it depends on living roots with enough oxygen.
Taught in How Trees Work, Lesson 10: Mineral absorption and the root environment
A bud that forms in an unusual place where no bud existed before, such as near a wound, on a root, or on older wood. The ability to form these buds varies greatly among trees.
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
The supply of air, especially oxygen, to roots through air-filled pore spaces, and the exchange of gases between those spaces and the open air. Roots need good aeration because their living cells use oxygen constantly.
Taught in How Trees Work, Lesson 2: Roots: anchorage, absorption, and storage
A form of layering done above ground: a ring of bark is removed or the stem is wounded and wrapped in moist material, and roots form at the upper edge of the wound, where sugars collect. The rooted part is later cut free and potted.
Taught in How Trees Work, Lesson 9: Sugar transport, storage, and demand
A leaf pattern with one leaf and one bud at each node, the nodes alternating sides or spiraling around the stem, as in ficus and elms. Growth after a cut tends to come as single shoots pointing in different directions.
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
Without oxygen, or describing a process or organism that works without it. A root zone that becomes anaerobic forces roots to rely on fermentation. The waterlogging that usually causes it also favors some root-rot organisms, such as water molds, which attack the weakened roots.
Taught in How Trees Work, Lesson 7: Respiration: powering living cells
The way roots hold a tree firmly in place against wind, gravity, and its own weight, mainly through the spread and grip of its structural roots. A shallow bonsai pot offers little anchorage, which is one reason newly potted trees are often secured with wire or ties.
Taught in How Trees Work, Lesson 2: Roots: anchorage, absorption, and storage
The tendency, across a whole tree, of the leading shoot and upper branches to restrain the growth of the branches below them. Its strength varies among trees and with age; together with shading, it helps explain why lower and interior bonsai branches can weaken over time.
Taught in How Trees Work, Lesson 12: How trees grow and change shape
The tendency of an actively growing shoot tip to hold back the buds below it, mainly through the hormone auxin moving down the stem along with other signals. Removing the tip often releases one or more of the buds below it to grow.
Taught in How Trees Work, Lesson 12: How trees grow and change shape
The group of dividing cells at the tip of a shoot or root that makes new cells for growth in length. In a shoot it also forms new leaves, nodes, and buds.
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
Short for adenosine triphosphate, a small molecule that carries usable energy within cells. Respiration makes ATP from the energy in sugars, and cells spend it to grow, repair themselves, and take up mineral nutrients.
Taught in How Trees Work, Lesson 7: Respiration: powering living cells
A plant hormone made mainly in shoot tips and young leaves that moves down the stem and helps control growth, including holding back buds below the tip and encouraging roots to form. It is the active ingredient in many rooting powders.
Taught in How Trees Work, Lesson 12: How trees grow and change shape
The growth of new shoots on older wood behind the current foliage, from latent buds or newly formed ones. Many broadleaves do it readily when vigorous and well lit, while many conifers, such as most junipers and pines, rarely do so on bare, older wood.
Taught in How Trees Work, Lesson 12: How trees grow and change shape
Everything outside the wood of a trunk, branch, or root: a protective, mostly dead outer layer and a thin, living inner layer beneath it. Because the inner layer carries sugars, damaged bark can harm a tree even when the wood underneath is intact.
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
A woody plant, usually a tree or shrub, grown in a container and shaped over many years so it suggests a mature tree at a small scale. The word is Japanese, roughly “planted in a tray or pot,” and names a practice, not a kind of plant.
Taught in How Trees Work, Lesson 1: A bonsai is a living tree
A thin layer of slow-moving, more humid air next to the surface of a leaf or needle, which slows the escape of water vapor into the open air. Wind thins this layer, increasing water loss.
Taught in How Trees Work, Lesson 8: Water transport and transpiration
A flowering tree or shrub with flat, typically broad leaves, such as a maple, elm, oak, or ficus, as distinct from a conifer. Broadleaves can be evergreen or deciduous, tropical or temperate, so the label alone does not tell you how to care for one.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
A compact, undeveloped shoot, flower, or both, containing a growing tip and tightly folded young leaves or flower parts, often protected by overlapping scales. Buds mark the places where new shoots can appear.
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
The stage when buds swell and open and new leaves or shoots begin to emerge, marking the start of a growth period. In deciduous temperate trees it is fueled at first largely by stored reserves.
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
A ring of narrow, crowded scars around a stem, left where a bud's protective scales fell away as it opened. Each ring marks where a flush of growth began, often once a year, so on many trees you can count recent years of growth along a twig.
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
The stage when shoots stop extending and form well-developed, often scale-covered buds that will carry the next season's growth. In many temperate trees, shortening days and cooler temperatures help trigger it in late summer or autumn.
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
Sugars and the larger compounds built from them, such as starch and cellulose, all made of carbon, hydrogen, and oxygen. Trees make their own carbohydrates from carbon dioxide and water using light energy, then use them as both building material and fuel.
Taught in How Trees Work, Lesson 1: A bonsai is a living tree
The ability of some soil and substrate particles to hold positively charged nutrient ions, such as potassium, calcium, and magnesium, on their surfaces and release them into the surrounding water in exchange for other ions. It helps a substrate store nutrients between fertilizer applications.
Taught in How Trees Work, Lesson 10: Mineral absorption and the root environment
A tough carbohydrate made of long chains of glucose units that forms the main framework of plant cell walls. It is the largest component of wood, and like all of a tree's carbohydrates, it comes from sugars made in photosynthesis.
Taught in How Trees Work, Lesson 6: Photosynthesis: building carbohydrates
The amount of time a temperate tree's buds must spend in cool weather before endodormancy ends and normal bud break can follow. Temperatures a few degrees above freezing count most, and hard cold counts for less. Requirements vary widely among trees; without enough chilling, bud break is often delayed, uneven, and weak.
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
The green pigment in chloroplasts that absorbs light, most strongly red and blue, and passes its energy into sugar-making. It absorbs green less strongly, so leaves reflect and transmit more green than other colors and look green, though a leaf still absorbs most of the green light that reaches it.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
A tiny green structure inside leaf cells and other green cells where light energy is used to make sugars from carbon dioxide and water. It holds chlorophyll, the pigment that captures that light.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
Yellowing of leaves that should be green, caused by too little chlorophyll. It is a symptom, not a diagnosis: nutrient shortages, damaged or waterlogged roots, high pH, and other problems can all cause it.
Taught in How Trees Work, Lesson 10: Mineral absorption and the root environment
The widely accepted explanation of how water rises in trees: evaporation from leaves pulls on water in the xylem, and because water molecules cling to each other and to cell walls, the pull passes down unbroken columns to the roots. The tree does not pump water upward.
Taught in How Trees Work, Lesson 8: Water transport and transpiration
The gradual process, triggered by shortening days and falling temperatures, in which a tree's tissues become able to survive freezing. A tree moved suddenly from a warm room into frost has not acclimated and can be badly damaged. It is not the same as shoots hardening, or turning woody, though the two often happen around the same time.
Also called: cold hardening
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
A tree's response to a wound: it forms chemical and anatomical boundaries that wall off the damaged wood and resist the spread of decay. The damaged tissue is sealed off, not repaired; CODIT, the name of the model that describes this, stands for “compartmentalization of decay in trees.”
Also called: CODIT
Taught in How Trees Work, Lesson 14: Stress, vigor, and recovery
A tree or shrub that bears seeds in cones, which are berrylike in junipers, instead of in flowers and fruits, and usually has needle-like or scale-like leaves. Most conifers are evergreen, but larches and a few others drop their needles each autumn.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
One of the first leaves of a plant, already formed in the embryo, which may store reserves or absorb them from surrounding tissue. Maples have two and pines often have several; in many trees they emerge, turn green, and photosynthesize.
Also called: seed leaf
A cultivated variety: a plant selected for particular traits, such as compact growth, small leaves, or unusual color, and kept consistent through propagation, often by cuttings or grafting. Cultivar names appear in single quotes, as in Juniperus procumbens ‘Nana’.
Taught in How Trees Work, Lesson 1: A bonsai is a living tree
A thin, waxy, water-resistant film covering the outer surface of leaves, needles, and young stems. It greatly slows water loss through the leaf surface, so most of a leaf's water vapor escapes through the stomata instead.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
Describes a tree that drops all its leaves for part of each year, usually before winter or a dry season, and grows new ones when growth resumes. Most deciduous trees are broadleaves, like the trident maple, but a few conifers, such as larches, are deciduous too.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
A gradual loss of health and growth over months or years, usually from several stresses acting together, such as poor light, root problems, or a missing winter rest. Early signs are subtle, so comparing dated records over time helps catch it.
Taught in How Trees Work, Lesson 14: Stress, vigor, and recovery
The progressive death of shoots, branches, or roots, usually starting at the tips and moving back toward older parts. It is a symptom with many possible causes, such as root damage, drought, frost, disease, or removing all foliage from a branch that cannot regrow.
Taught in How Trees Work, Lesson 14: Stress, vigor, and recovery
A period when a tree, bud, or seed is alive but not growing, held back by its own internal controls, by outside conditions such as cold, or, for a bud, by an actively growing shoot tip above it. Dormant trees still respire and still need moisture, protection, and attention.
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
The phase of dormancy after the chilling requirement has been met, when buds are able to grow but cold or other outside conditions still hold them back. Rising warmth then brings bud break.
Also called: quiescence
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
A blockage in a xylem pipe caused by an air bubble that breaks its water column, often during severe drought or after freezing and thawing. A blocked pipe stops carrying water, so the tree relies on its other pipes and on new wood to replace that capacity.
Taught in How Trees Work, Lesson 8: Water transport and transpiration
The tiny, partly formed young plant inside a seed, with a first root, a short stem, a shoot tip, and one or more seed leaves. It is alive but largely inactive until germination.
The deep phase of dormancy in which buds will not grow even if conditions turn warm, because signals within the buds hold them back. In most temperate trees it ends only after enough time at cool temperatures, the tree's chilling requirement.
Also called: rest
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
A tissue in many flowering-plant seeds that stores reserves and supplies them to the embryo during germination. Some seeds, such as maples, keep their reserves mainly in the cotyledons instead, and pine seeds hold theirs in a similar storage tissue.
How strongly the surrounding air draws water vapor from leaves, rising with sun, heat, dry air, and wind. High evaporative demand can make a tree lose water faster than reduced or damaged roots can replace it.
Taught in How Trees Work, Lesson 8: Water transport and transpiration
Describes a tree that keeps living foliage all year, replacing old leaves or needles gradually instead of all at once. Keeping foliage does not mean a tree grows all year: temperate evergreens such as junipers still go dormant in winter.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
A way of releasing energy from sugar without oxygen, which yields far less usable energy than respiration with oxygen and produces byproducts that can harm cells as they accumulate. Roots in persistently saturated media fall back on it and can run short of energy.
Taught in How Trees Work, Lesson 7: Respiration: powering living cells
A product that supplies mineral nutrients, such as nitrogen, phosphorus, and potassium, for roots to absorb. It supplies no energy or carbohydrates that the tree can use, so it cannot make up for too little light or too few healthy leaves, and too much can harm roots.
Taught in How Trees Work, Lesson 6: Photosynthesis: building carbohydrates
One of the many thin, branching roots, often pale when young, that do most of a tree's absorbing of water and mineral nutrients. Fine roots live a relatively short time and are constantly replaced, so they depend on a root zone that holds both water and air.
Also called: feeder root
Taught in How Trees Work, Lesson 2: Roots: anchorage, absorption, and storage
The stage when a bud begins forming flowers instead of only leaves and shoots. In many spring-flowering trees it happens during the previous growing season, so pruning at the wrong time can remove next year's flowers.
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
A burst of new shoot growth, with leaves expanding together, that happens once or several times a year depending on the tree and conditions. Between flushes, shoots stop extending and mature.
Taught in How Trees Work, Lesson 12: How trees grow and change shape
A tree's leaves or needles considered together: the living surfaces where light is captured, carbohydrates are made, and gases and water vapor pass to and from the air. The amount, health, and light exposure of the foliage largely set how much carbohydrate a tree can make, one of the main limits on its growth.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
The movement of gases between a plant's tissues and the surrounding air. In leaves it happens mainly through stomata, as carbon dioxide and oxygen pass in and out and water vapor escapes; roots and stems also take in oxygen from the air around them.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
The process in which a seed's embryo resumes growth and breaks out of the seed, beginning with water uptake and usually marked by the young root emerging. It needs water, oxygen, and a suitable temperature, and some seeds also need light, darkness, or a dormancy treatment first.
Damage that removes or crushes a complete ring of bark around a trunk, branch, or root, severing the phloem all the way around. Sugars from the leaf side can no longer pass, so tissues on the root side lose that supply; a fully girdled trunk usually kills the tree over time.
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
A simple sugar that plants form through photosynthesis and use both as fuel and as a basic building unit. Trees link many glucose units together to make starch for storage and cellulose for cell walls.
Taught in How Trees Work, Lesson 6: Photosynthesis: building carbohydrates
A band of wood laid down during one period of growth, seen in a cross-section as lighter, more open early wood followed by denser late wood. In many temperate trees each ring marks one year, but rings can be faint or irregular, especially in tropical trees.
Also called: annual ring
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
One of the two curved cells around each stoma that swell with water to open the pore and lose water to close it. Guard cells balance carbon dioxide intake against water loss, responding to light, carbon dioxide, the leaf's water supply, and the hormone abscisic acid, which leaves make as water runs short and which may also arrive from drying roots.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
The inner, older wood at the center of many trunks and large branches, which no longer carries water and has no living cells. It is often darker from deposited compounds that can help resist decay; not every tree forms distinct heartwood.
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
The short stem of a seedling between its young root and its seed leaves. In many trees it lengthens as a hook that pulls the seed leaves up through the soil, then straightens.
An oxygen supply too low for cells to respire normally. In containers it most often affects roots when the substrate stays saturated, because oxygen moves through water roughly ten thousand times more slowly than through air.
Also called: low oxygen
Taught in How Trees Work, Lesson 7: Respiration: powering living cells
The first step of germination, when a dry seed soaks up water and swells. In a living seed this restarts metabolism, but the uptake is largely physical, so a dead seed can swell too. A seed with a hard, waterproof coat cannot take up water this way until the coat is cracked or worn.
The living layer between the outer bark and the wood, made mostly of phloem, the tissue that carries sugars. It is thin, soft, and close to the surface, so wire, tools, and careless handling can readily damage it.
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
The stretch of stem between two neighboring nodes. Internodes tend to be longer in vigorous or shaded growth and shorter in slow growth or strong light, and short internodes help a bonsai's branches look finer and more compact.
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
An atom or small group of atoms carrying an electric charge, positive or negative, such as potassium, calcium, or nitrate. Roots absorb mineral nutrients as ions dissolved in the water around them.
Taught in How Trees Work, Lesson 10: Mineral absorption and the root environment
The early phase of a tree's life when it cannot yet reproduce, by flowering or bearing cones, however well it grows. It can last from a few years to decades depending on the tree. Many junipers grow needle-like foliage when young, but foliage shape alone does not show whether a juniper is mature enough to bear cones.
Also called: juvenile phase
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
A bud that stays inactive beyond its first season, often for years, and may lie hidden beneath the bark of older wood. It may grow after a disturbance such as pruning, which is one source of new shoots on older branches. Growers sometimes call these dormant buds, but any bud resting through winter is dormant.
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
A bud on the side of a stem, formed in the angle where a leaf joins the stem. Lateral buds can grow into side shoots, often after the shoot tip above them is removed or slows.
Also called: axillary bud
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
A way of making a new plant by encouraging roots to form on a stem while it is still attached to, and watered through, the parent plant, then separating it once it has roots of its own.
Taught in How Trees Work, Lesson 9: Sugar transport, storage, and demand
The angle on the upper side where a leaf joins its stem. A lateral bud usually forms there, which is why buds sit right above leaves, or above the scars left by fallen leaves.
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
The mark left on a stem where a leaf was attached before it fell, often crescent- or shield-shaped, usually with a bud right above it. Leaf scars help you find the nodes on a bare winter twig.
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
A stiff, complex compound deposited in the cell walls of wood and other supporting tissues, making them rigid and water-resistant. Trees build lignin from compounds they make from sugars, so it, too, comes ultimately from photosynthesis.
Taught in How Trees Work, Lesson 6: Photosynthesis: building carbohydrates
Whichever necessary resource or condition, such as light, water, carbon dioxide, temperature, or a mineral nutrient, is in shortest supply and so caps how fast a process like photosynthesis can go. Adding more of anything else brings little benefit until it is addressed.
Taught in How Trees Work, Lesson 6: Photosynthesis: building carbohydrates
A mineral nutrient that plants need in relatively large amounts: nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Nitrogen, phosphorus, and potassium are the three behind the N-P-K numbers on fertilizer labels.
Taught in How Trees Work, Lesson 10: Mineral absorption and the root environment
The carrying of dissolved nutrients toward roots by moving water, as roots take up water to replace what the leaves lose. It delivers nutrients such as nitrate and calcium, while others, such as phosphate, reach roots mostly by slow diffusion.
Taught in How Trees Work, Lesson 10: Mineral absorption and the root environment
A group of plant cells that keep dividing to produce new cells, found at the tips of shoots and roots, inside buds, and in thin layers beneath the bark. All of a tree's new growth, in length or in thickness, starts in a meristem.
Taught in How Trees Work, Lesson 2: Roots: anchorage, absorption, and storage
The inner tissue of a leaf between its upper and lower surfaces, packed with chloroplast-rich cells where most photosynthesis happens. Loosely arranged cells with air spaces between them let carbon dioxide reach every cell.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
A mineral nutrient that plants need only in tiny amounts, such as iron, manganese, zinc, copper, or boron. Tiny amounts are still essential: a shortage of iron, for example, can yellow new leaves between their veins.
Taught in How Trees Work, Lesson 10: Mineral absorption and the root environment
A chemical element, such as nitrogen, potassium, or iron, that a tree needs and takes up through its roots from the water around them. Mineral nutrients help build and run cells, but they supply no energy and only a small share of the tree's mass.
Taught in How Trees Work, Lesson 1: A bonsai is a living tree
A tiny structure (plural: mitochondria) inside nearly every plant and animal cell where respiration releases most of the usable energy from sugars, using oxygen. Every living cell in a tree relies on its mitochondria, including root cells that never see light.
Taught in How Trees Work, Lesson 7: Respiration: powering living cells
A partnership (plural: mycorrhizae) between a plant's roots and certain soil fungi, known as mycorrhizal fungi, whose fine threads reach far beyond the roots and help supply water and nutrients, especially phosphorus, in exchange for sugars from the plant. Many trees, including pines, depend heavily on these partnerships.
Taught in How Trees Work, Lesson 10: Mineral absorption and the root environment
The point on a stem where one or more leaves attach, usually with a bud in the angle of each leaf. New shoots most often grow from nodes, so they show where a cut can leave a growth option behind.
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
Whether a mineral nutrient in the root zone is dissolved, in a form roots can take up, and close enough to reach them, which depends on the conditions around the roots, such as moisture, pH, and the substrate itself. A nutrient can be present in the substrate yet unavailable to the tree, and an available nutrient still has to be absorbed by living roots.
Taught in How Trees Work, Lesson 10: Mineral absorption and the root environment
A leaf pattern in which two leaves, each with a bud, grow from the same node on opposite sides of the stem, as in maples. Cutting above such a node can produce a pair of shoots.
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
The outermost layer of a trunk or branch, made of dead tissue, chiefly cork, added from the inside by a thin living layer called the cork cambium. On older trunks it also holds older bark tissues cut off as new cork forms beneath them. It shields the living tissues inside from water loss, injury, temperature extremes, and disease organisms.
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
The Chinese art of growing and shaping trees, and sometimes whole miniature landscapes with rocks and water, in containers. It is the older tradition from which bonsai developed in Japan.
Taught in How Trees Work, Lesson 1: A bonsai is a living tree
A scale, usually 0 to 14, that measures how acidic or alkaline a solution or substrate is: 7 is neutral, lower numbers are acidic, and higher numbers are alkaline. It affects which mineral nutrients stay dissolved and available to roots.
Taught in How Trees Work, Lesson 10: Mineral absorption and the root environment
The timing of a plant's recurring life events through the year, such as bud break, flowering, leaf color change, leaf fall, and dormancy, and how weather and climate shift them. Timing care to these stages works better than following calendar dates.
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
The living tissue that carries dissolved sugars and other compounds from where they are made or stored to where they are needed, such as roots, shoot tips, and storage tissues. In trunks and branches it forms the inner bark, and its flow can run upward or downward.
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
The length of daylight in each 24-hour day, which changes with the seasons and acts as a calendar signal for plants. Shortening days help tell many temperate trees to stop growing, set buds, and prepare for winter.
Also called: day length
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
The process in which green plant cells use light energy to combine carbon dioxide from the air with water, making sugars and releasing oxygen. It is how a tree makes the carbohydrates that it builds with and runs on.
Taught in How Trees Work, Lesson 6: Photosynthesis: building carbohydrates
The small core of soft tissue at the very center of a stem, formed when that part of the stem first grew as a young shoot. In older trunks and branches it remains as a narrow center surrounded by many layers of wood.
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
The gaps between particles in soil or substrate, which hold water, air, or both. Large pores usually drain and refill with air after watering while small pores hold water, so the mix of pore sizes sets how wet and how airy a root zone stays.
Taught in How Trees Work, Lesson 2: Roots: anchorage, absorption, and storage
The main explanation of how phloem moves sugar: loading sugar into the phloem at a source draws in water, raising pressure that pushes the sugar solution along to sinks, where the sugar is unloaded and the water leaves.
Taught in How Trees Work, Lesson 9: Sugar transport, storage, and demand
Growth in length at the tips of shoots and roots, produced by apical meristems, which also forms new leaves, nodes, and buds. It is how a branch extends and how a root explores new substrate.
Taught in How Trees Work, Lesson 12: How trees grow and change shape
The young root of a seed's embryo, usually the first part to emerge during germination. It grows downward to become the seedling's first root.
A tree's return toward normal growth and function after stress or work such as repotting or heavy pruning, drawing on its remaining leaves, roots, and reserves. It takes time that cannot be guaranteed, and fertilizer cannot speed it beyond what roots and light allow.
Taught in How Trees Work, Lesson 14: Stress, vigor, and recovery
Carbohydrates, mostly starch, stored in living cells of the roots, trunk, branches, and bark for later use. Reserves fuel early spring growth before new leaves can supply sugar, and they help a tree recover after losing foliage or roots. A seed carries reserves of its own, such as starch, oils, and proteins, that fuel the embryo's first growth.
Also called: carbohydrate reserves
Taught in How Trees Work, Lesson 9: Sugar transport, storage, and demand
The process in which living cells break down sugars using oxygen to release energy they can use, giving off carbon dioxide and water. It runs in every living cell of a tree, in leaves, stems, buds, and roots, both day and night. Without oxygen, cells fall back on fermentation.
Also called: cellular respiration
Taught in How Trees Work, Lesson 7: Respiration: powering living cells
A thimble-shaped cover of cells over the very end of a root that protects the dividing cells behind it as the root pushes through soil, and senses gravity to help steer its growth. Its living outer cells release a slimy coating, called mucilage, that eases the root's path, and they wear away and are replaced from within.
Taught in How Trees Work, Lesson 2: Roots: anchorage, absorption, and storage
A tiny, hairlike outgrowth of a single cell on a root's surface, a short way behind the growing tip, that greatly increases the area for absorbing water and minerals. Some trees, such as pines, grow few and rely more on fungal partners. Root hairs are fragile and short-lived, so disturbing roots destroys many of them and temporarily reduces uptake.
Taught in How Trees Work, Lesson 2: Roots: anchorage, absorption, and storage
All of a tree's roots together, from the thick woody roots near the trunk to the many thin roots at the edges. It anchors the tree, absorbs water and mineral nutrients, and stores carbohydrates; in a bonsai, all of it must fit inside a small container.
Taught in How Trees Work, Lesson 2: Roots: anchorage, absorption, and storage
The growing end of a root, made up of the root cap, the dividing cells behind it, and short zones where new cells lengthen and mature. Active tips are usually pale or white and show where a root is extending into fresh substrate.
Taught in How Trees Work, Lesson 2: Roots: anchorage, absorption, and storage
A branch deliberately allowed to grow long and leafy for a time, so its foliage supplies extra sugars that thicken the trunk below it and the roots, then removed once it has done its job. Its removal leaves a wound that the tree must grow over.
Taught in How Trees Work, Lesson 12: How trees grow and change shape
The outer, younger part of the wood, which carries water and dissolved minerals upward and contains living cells that store carbohydrates. It is usually paler than heartwood and is the part of the wood that is still working.
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
Describes soil or substrate whose pore spaces are completely filled with water, leaving little or no air. Brief saturation right after watering is normal in a pot that drains; saturation that lasts starves roots of oxygen.
Also called: waterlogged
Taught in How Trees Work, Lesson 7: Respiration: powering living cells
Weakening or breaking a hard, waterproof seed coat, for example by nicking it, rubbing it with sandpaper, or soaking it in hot water, so water can reach the embryo. It addresses only coat-imposed dormancy, so some seeds need both scarification and stratification.
Growth in thickness of stems and roots, produced mainly by the vascular cambium adding wood on its inside and phloem on its outside, while a separate layer renews the outer bark. It depends on sugars made by the foliage, used as they are made or drawn from stored reserves.
Taught in How Trees Work, Lesson 12: How trees grow and change shape
A small package a plant produces to start a new generation, containing a living embryo, stored reserves to fuel its first growth, and a protective outer coat. There are no special bonsai seeds; kits contain ordinary tree seeds.
The protective outer layer of a seed, which shields the embryo from drying, injury, and decay. In some seeds it is hard and waterproof, so water cannot enter until it is cracked, worn, or broken down.
A state in which a living seed will not germinate, even in good conditions, until a specific requirement is met, such as a period of cold, moist conditions or a break in a hard seed coat. It differs from a seed failing to germinate because conditions are wrong.
A young plant raised from seed, especially in its early, fragile stages after germination. Years usually pass before a seedling has a trunk worth styling, which is why growing from seed is a long-term option rather than a starting requirement.
Any part of a tree that uses or stores more sugar than it makes, such as growing shoot tips, young leaves, the cambium, roots, flowers, fruits, and storage tissues while they fill. Phloem carries sugar from sources toward sinks.
Taught in How Trees Work, Lesson 9: Sugar transport, storage, and demand
Dissolved minerals, from fertilizer and from tap water, that can accumulate in a container's substrate as water evaporates. A high concentration makes it harder for roots to take up water and can damage them. Buildup can leave a white crust on the pot or surface, though hard tap water alone can leave a similar crust, so a crust by itself does not show that roots are harmed.
Also called: salt buildup
Taught in How Trees Work, Lesson 10: Mineral absorption and the root environment
Any part of a tree that makes or releases more sugar than it uses, so it exports sugar to other parts, such as a mature leaf in good light or storage tissue turning its starch back into sugar. Whether a part acts as a source can change with its age and the season.
Taught in How Trees Work, Lesson 9: Sugar transport, storage, and demand
A group of closely related plants or animals that share distinctive features and usually breed with one another, given a two-part scientific name such as Acer buergerianum for the trident maple. Knowing a tree's species tells you much about its growth and care.
Taught in How Trees Work, Lesson 1: A bonsai is a living tree
A carbohydrate made of many glucose units linked together, which plants use to store energy and building material. Trees store starch in living cells of roots, wood, and bark, then convert it back to sugar to fuel spring growth and recovery.
Taught in How Trees Work, Lesson 6: Photosynthesis: building carbohydrates
A microscopic pore (plural: stomata), mostly on leaves and needles, through which gases pass in and out, chiefly carbon dioxide entering and water vapor leaving. A pair of guard cells widens or narrows each pore in response to light, the water supply, and the surrounding air.
Also called: stomate
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
A pretreatment that holds seeds in moist conditions at a set temperature, most often cool but above freezing (cold stratification), for weeks or months to break the dormancy that many temperate tree seeds have. The needed length and temperature vary with species and seed source.
Any condition that pushes a tree's functioning outside its normal range and limits growth or survival, such as drought, waterlogging, heat, cold, poor light, root loss, pests, or heavy pruning. Several stresses at once can add up to more than the tree can support.
Taught in How Trees Work, Lesson 14: Stress, vigor, and recovery
A thick, woody, long-lived root that anchors the tree, stores carbohydrates, and connects the fine roots to the trunk, conducting water and sugars along its length. Structural roots absorb relatively little water compared with young fine roots.
Taught in How Trees Work, Lesson 2: Roots: anchorage, absorption, and storage
The material that fills a container and surrounds a tree's roots, such as a mix of mineral grit, bark, or soil. Its job is to anchor the roots and to hold water, mineral nutrients, and air in a balance the roots can use.
Also called: growing medium, bonsai soil
Taught in How Trees Work, Lesson 2: Roots: anchorage, absorption, and storage
Describes regions bordering the tropics, with hot summers and mild winters that bring occasional cool spells or light frost, and the plants adapted to them. Subtropical trees typically have little or no chilling requirement but may tolerate cooler weather than tropical ones.
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
The narrowing of a trunk or branch from its thick base toward its tip, which helps a tree look mature and natural. Stems thicken more where they support and connect more foliage, so a single retained branch thickens the trunk below it, with a fairly sudden change in width at its junction, while smooth, gradual taper is usually built over years by growth at several heights.
Taught in How Trees Work, Lesson 12: How trees grow and change shape
Describes regions with distinct warm and cold seasons, and the trees adapted to them, which typically need a cool winter rest. Trident maples and the junipers commonly grown as bonsai are temperate trees and need seasonal outdoor conditions rather than a warm room all year.
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
The bud at the tip of a shoot, which continues that shoot's growth in length when it opens. While it is actively growing, it tends to hold back the buds below it.
Also called: apical bud
Taught in How Trees Work, Lesson 5: Buds, nodes, and growing points
A long, narrow, hollow xylem cell, dead when working, with tapered ends that pass water to neighboring cells through small pits in their walls. Conifer wood is made mostly of tracheids, which both conduct water and support the tree.
Taught in How Trees Work, Lesson 8: Water transport and transpiration
The movement of sugars and other dissolved compounds through the phloem from sources to sinks, in whichever direction the demand lies. It can carry sugar up to a growing shoot and down to the roots at the same time.
Taught in How Trees Work, Lesson 9: Sugar transport, storage, and demand
The evaporation of water from inside a plant and its escape as vapor, mostly through the stomata of leaves. As water evaporates, more is pulled up from the roots through the xylem; most of the water a tree absorbs is lost this way.
Taught in How Trees Work, Lesson 4: Leaves and needles: working surfaces
Describes warm regions near the equator without a cold winter, and the trees adapted to them. Tropical trees such as ficus have no chilling requirement and can be damaged or killed by frost; their growth slows when light or warmth drops.
Taught in How Trees Work, Lesson 13: Growth cycles, dormancy, and reproduction
One of the leaves a seedling's shoot tip forms after its seed leaves, usually closer in shape to the plant's typical foliage. Young true leaves import sugar at first and export it once they mature. Many seedlings come to rely more on their own photosynthesis than on seed reserves around the time true leaves appear, though the timing varies by species.
The pressure of water inside plant cells pushing against their walls, which keeps soft tissues such as leaves and young shoots firm. When cells lose water faster than they gain it, turgor drops and the tissues go limp.
Taught in How Trees Work, Lesson 8: Water transport and transpiration
A layer of dividing cells, only a few cells thick, between the wood and the inner bark. It adds new xylem on its inner side and new phloem on its outer side, which is how trunks, branches, and roots grow thicker.
Also called: cambium
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
The tree's transport tissues, xylem and phloem, which run in connected strands and layers from just behind the root tips through the trunk and branches into every leaf. Xylem carries water and dissolved minerals; phloem carries sugars.
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
A long tube in the xylem of most broadleaf trees, made of hollow, dead cells joined end to end with open or perforated end walls. Their width lets vessels move water quickly.
Taught in How Trees Work, Lesson 8: Water transport and transpiration
Whether a seed is alive and able to germinate under the right conditions. Viability falls with age and poor storage, and some seeds, such as many acorns, die if they dry out.
A tree's observed growth performance relative to its expected seasonal behavior, meaning what a tree of its kind should be doing at that point in the season. It is judged from shoot extension, bud development, foliage condition, and root activity when visible, across several observations over time, not from one large leaf or green color. A vigorous tree is growing at or above that expected pace.
Taught in How Trees Work, Lesson 14: Stress, vigor, and recovery
A measure of water's tendency to move from one place to another, lowered by dissolved substances, by suction, and by attraction to surfaces. Water moves from higher to lower water potential, which is why it flows from moist substrate, through the tree, into drier air.
Taught in How Trees Work, Lesson 8: Water transport and transpiration
Drooping of leaves or soft shoots when their cells lose turgor because water loss has outpaced uptake. It can come from a dry root zone, but also from damaged or reduced roots, very high demand, or blocked xylem, even when the substrate is wet.
Taught in How Trees Work, Lesson 8: Water transport and transpiration
Damage that occurs when a branch thickens against bonsai wire, which cannot stretch, so the coils press into the bark and the living tissues beneath. It can restrict sugar transport and leave spiral scars that last for years.
Also called: wire scar
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
The hard interior of trunks, branches, and older roots, made of layer upon layer of xylem added by the vascular cambium. The outer, younger wood carries water and stores reserves, while the inner wood in many trees no longer conducts and mainly gives support.
Also called: secondary xylem
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport
A plant, such as a tree, shrub, or woody vine, whose stems live above ground from year to year and grow thicker by adding layers of hard, long-lived tissue. Every bonsai is an ordinary woody plant, not a special kind of plant.
Taught in How Trees Work, Lesson 1: A bonsai is a living tree
The gradual covering of a wound's exposed surface as woundwood grows in from its edges until the edges meet. Its speed depends on the tree's vigor, the wound's size and position, and the kind of tree; large wounds may never fully close.
Taught in How Trees Work, Lesson 14: Stress, vigor, and recovery
New wood and bark that grow from the living edges of a wound, forming a rounded roll that gradually spreads over the exposed surface. It covers the wound but does not restore the damaged wood beneath. Bonsai growers often call it callus, though strictly callus is the soft tissue that forms first at a wound's edge, before woundwood.
Also called: callus
Taught in How Trees Work, Lesson 14: Stress, vigor, and recovery
The tissue that carries water and dissolved minerals from the roots up through the trunk and branches to the leaves, mostly through hollow cells that are dead when they work. Built up in layers year after year, xylem makes up a tree's wood.
Taught in How Trees Work, Lesson 3: Trunks and branches: structure and transport