Formation of a root or shoot (bud) from other than naturally occurring sequential branching of a seedling root or shoot system, respectively; i.e. adventitious roots are those which develop on stems or leaves, while adventitious shoots are those which arise on roots (suckering), or on stems, from other than lateral buds. Either adventitious roots and/or buds may also develop in vitro from undifferentiated callus tissue in some micropropagation systems.

One of the two or more (e.g. dominant and recessive) forms of a gene at the same locus on homologous chromosomes.



Alternation of generations
Refers to the alternation between a haploid (n) gametophyte phase and a diploid (2n) sporophyte phase in the lifecycle of sexually reproducing organisms.

Apomixis (n.) Apomictic (adj)
The process of asexual embryo development within a seed arising from mitotic division of maternal cells rather than the meiotic cell division and gamete fusion typical of sexual embryos. Apomictic embryos are genetically identical (clonal) to the parent plant from which they come.

Plant tissue and associated environment free of microorganisms; characteristic of most micropropagation systems.

A naturally occurring or synthetic plant hormone which stimulates cell elongation, root formation and other physiological processes.

The outer layers of a woody plant stem external to the vascular cambium, including the periderm (outer bark) and phloem (inner bark).


Breeding system
Natural reproductive strategy, including either inbreeding (sexual), outbreeding (sexual), apomixis (asexual), or other means of asexual reproduction (eg. runners, suckers, etc.).

A mass of large thin walled plant cells (mainly parenchyma) occurring at wounds; such as at the base of a cutting or at the stock/scion union of a grafted plant.


Carbohydrate; chief component of the cell wall in plants.



Structure in the cell nuclei that carries the genetic material contained within the genes. Eukaryotic chromosomes are visualized as threads or rods of chromatin, consisting of a linear sequence of genes, which appear in contracted form during mitosis and meiosis, and otherwise are enclosed in a nucleus.


Found in eukaryotic chromosomes; a complex of DNA and proteins that readily stains.



The set of all individual organisms (plants) produced by asexual propagation from one sexually propagated individual (stock plant).

A named assemblage of plants, not found in nature, which have some set of agriculturally desirable traits, and which come true to type when propagated. Some cultivars can only be propagated vegetatively in order to maintain the defining characteristics, while others come true from seed.



Propagation by the rooting of cuttings.



Protoplasm (living substance) of a cell exclusive of the nucleus.

De novo
Newly developed in response to some external stimulus; not naturally occurring (e.g. root formation on a cutting).

A seed cleaning practice which involves removal of the extension of a seed coat or persistent ovary wall (wing) which protrudes out from the main body of a seed and is usually involved in seed dispersal by wind.

Moisture loss (drying) by transpiration or evaporation of whole plants, seeds or plant parts such as cuttings, scions, etc.



Modification of tissues in structure or function as the result of an increase in specialization.



Each cell containing two sets of chromosomes; the 2n (diploid) chromosome number is characteristic of the sporophyte generation.



Deoxyribonucleic acid; carrier of genetic information in cells and viruses; is capable of self-replication.

Double Working
A three part grafted plant consisting of a scion, an interstock, and a rootstock, with a graft union between scion and interstock and between interstock and rootstock.



Of or influenced by the soil.



Plant development in the absence of light, which is characterized by lack of chlorophyll development (yellow rather than green color of leaves and stems), internode elongation, and small unexpanded leaves.


Applying to cells that have a membrane-bound nucleus, membrane-bound organelles, and chromosomes in which the DNA is associated with proteins; an organism made up of these types of cells.

Field capacity
The maximum moisture content of a soil when it has been watered to excess and allowed to drain by gravity.



Male or female reproductive cell;germ cell; microspore; pollen (male); megaspore or ovule (female); haploid reproductive cell; gametes fuse in pairs, forming zygotes, which are diploid; product of meiosis.

Gametophyte Generations
In plants exhibiting an Alternation of Generations lifecycle, the haploid (n), gamete-producing phase.

The genetic composition of an organism. i.e. the DNA sequence in plants and animals.


Growth phase
The physiological (not chronological) "age" of a plant with respect to its ability to flower, viz. Juvenile phase is unable to flower, regardless of environmental conditions; adult or mature phase is capable of flowering under inductive environmental conditions. Secondary characteristics of growth phase may include ease of vegetative propagation associated with juvenility, and in some cases (species specific), differences in leaf morphology, and/or other morphological characteristics. Cyclophysis refers to both growth phases occuring on the same seedling-derived plant.



Having only one set of chromosomes (n), as in gametophtes, in contrast to diploid 2(n), as in sporophytes.


Producing two kinds of spores, microspores and megaspores.


Heterozygosity / Heterozygous
A preponderance of genes in a plant genome with dissimilar alleles; giving rise to high level of variability in the next generation of seedlings.

Grafting high up in the canopy of tree, usually to create an unusual growth form.

A genetic condition in which similar alleles occur at one or more loci.

The 1st stage of seed germination involving uptake of water.

In vitro
In a tissue culture / micropropagation system; literally "in glass".

failure of stock and scion to form a successful graft union due to insufficiently close genetic relationship

Deliberate self pollination, through several generations, of a naturally outcrossing species, giving rise to increasingly homozygous genotype

Layering (Layerage)
A method of asexual propagation (or natural reproduction) which invovles adventitious root formation on a stem while it is still attached to the intact stock plant. Some common types of layering incude air layering (marcottage), mound layering (stooling), tip layering, etc.

The process of wood formation whereby new nonwoody shoot growth becomes woody by deposition of lignin into the secondary cell walls of xylem cells.


An important ingredient of the secondary wall of vascular plants; an organic hardening substance; not all secondary walls contain lignin; after cellulose, lignin is the most abundant plant polymer.

Air layering



In heterosporous plants, spore (n) that develops into female gametophyte.


Process of two successive nuclear divisions; single diploid (2n) cell becomes four haploid (n) cells.

Cell division giving rise to haploid sex cells (gametes)

A group of undifferentiated cells which are capable of dividing indefinitely, and function to generate cells which subsequently differentiate into new growth. The primary meristems which are the apical shoot tip, and the root tip meristems function to produce elongation of the shoot and root respectively. The secondary meristem, known as the vascular cambium is a single layer of meristematic cells that occurr in a cylinder between the xylem and phloem, and which divide to produces some cell that push outward and differentiate into phloem, while others push inward and differentiate into xylem.



In heterosporous plants, spore that develops into male gametophyte.

Cell division giving rise to genetically identical, diploid, somatic cells, i.e. non-gamete cells of the plant body.



(1) A specialized body within the living eukaryotic cell bounded by a double membrane and containing the chromosomes; essential to the regulation and control of all the cell's functions.



Life or developmental history of part or all of an individual organism.



A specialized, membrane -bound body in the cytoplasm of a cell.

Stock plant from which propagules are obtained for asexual propagation.


The fertilization of an ovary by pollen from another plant, not the mother plant. This is the source for genetic diversity among species.



In seed plants, the structure that contains a female gametophyte; it has potential to develop into an embryo; when mature an ovule becomes a seed.


Parenchyma cells
Most abundant kind of cells in plants, usually thin-walled of variable size, shape, and function.

A disease causing microorganism (bacteria, fungus, or virus).

Seasonal changes in plant growth and development. E.g. the sequence from dormant bud, to bud swelling, to bud opening and flowering during the spring growth flush in temperate species.

The observable expression of a particular genotype under a given set of environmental conditions and developmental ontogeny. (stage of development).

Plant tissue and associated cells, located just to the outside of the vascular cambium, which is involved in translocation of carbohydrate products of photosynthesis and other organic and inorganic compounds from leaves and other source organs to roots and other sink organs of higher plants.



Day length.

Plant tissue composed mainly of parenchyma cells, located interior to the primary xylem in the stems of higher plants.


Derived from the microspore of seed plants, the structure that develops into a male gametophyte.

Development of more than one embryo within a single seed, usually as a result of apomixis.


Referring to an organism, tissue, or cell having more than two complete sets of chromosomes.


Development of reproductive maturity (ability to flower) sooner than is typical for the species.

Portion (ramet) of a stock plant (ortet) removed for asexual propagation; i.e. cutting, scion, explant.

Propagule; portion of an ortet detached for asexual propagation; i.e. cutting, scion, rooted layer, or explant.

Seed which is intolerant of drying and, in the case of temperate recalcitrant seed, also intolerant low temperature; hence limited storage life.

Outer plus inner bark (i.e. periderm + phloem), exterior to the vascular cambium, which seperates when the bark peels away from the underlying wood.



Rind Grafting
Any grafting technique which requires the bark to be slipping.


Seed stratification
Moist chilling of seeds to break dormancy and facilitate germination.

Sexual propagation
The process of sexual plant reproduction beginning with meiotic cell division and gamete (ovule and pollen) formation, followed by gamete fusion, embryo (seed) formation, and finally seed germination giving rise to seedlings.

Slipping (bark)
(Re: grafting) - peeling (rather than tearing) away of the bark (phloem plus periderm) from the underlying wood (xylem) of a stem, which occurs when the vascular cambium is actively growing.




Somatic cells
Vegetative, non-sexual; all cells in organism except the gametes and the cells from which the gametes develop.



A reproductive cell or aggregation of cells capable of developing into an adult without fusion with another cell.



Sporophyte Generation
The spore producing, diploid (2n) phase in a life cycle characterised by Alteration of Generations.

An off-type caused by a genetic mutation; often a single branch on an otherwise "wild type" tree, arising from a bud mutation.

(More properly termed pasteurization) - to free propagation media from disease-causing microorganisms by a variety of physical (steam or solarization) or chemical (fumigation) means.

Stock (rootstock, understock)
Lower portion of a grafted plant (including the root system) onto which the scion is grafted

Stomate (stomata, pl.)
An tiny variable sized opening between two guard cells on the surface of a leaf, which allows for gas exchange (carbon dioxide, in; water vapor, out) between the inside and outside of the leaf. The size (aperature) of the pore, varies with environmental conditions as a means of regulating transpiration. For example, drought stress causes stomatal closure, thus reducing moisture loss from the leaf. Light causes stomatal opening, thus promoting photosynthesis (carbon dioxide uptake).

Stooling (mound layering)
A type of layering in which rooting occurs at the base of ground level coppice shoots mounded with a moist soil or other medium (e.g. sawdust)

Occurring throughout the plant body, with the exception of primary shoot and root meristems

(Re: grafting) - formation of a successful graft or bud union.




Topworking (syn. highworking)
Any grafting method that is performed high up on the trunk, rather than near ground level. This may be only several feet for a small tree in a nursery, or far up in the canopy of an established tree in the field.

In plants, it refers to the transport of water, minerals, or food.

Water loss, primarily from stomates on the leaf surface. Transpirational "pull" (via cohesion) generates much of the force responsible for water (and dissolved nutrient) uptake from roots, and hence is a necessary function.

When progeny resulting from sexual or asexual propagation are genetically identical to the parent plant from which they were propagated.

Vascular cambium
A layer of plant cells which is permanently meristematic (capable of cell division). The vascular cambium lies between the xylem and phloem of a woody plant stem, and gives rise to new xylem and phloem by cell divisions to the inside and outside respectively.

Vivipary (seed)
Extreme lack of dormancy characterized by germination within the fruit (pod) while still attached to the parent tree.


A layer of cells, involved in the upward translocation and storage of water and minerals and mechanical support, which is located interior to the vascular cambium.

The diploid or polyploid single cell resulting from the fusion of male and female gametes. Subsequent mitotic cell division of the zygote leads to embryo development.