Calcareous – containing calcium, the source typically being chalk or limestone.
Calyx – outer part of a flower, comprising the sepals.
Capsule – dry fruit that splits to liberate its seeds.
Catkin – hanging spike of tiny flowers.
Clasping – descriptive of leaf bases that have backward-pointing lobes which wrap around the stem.
Compound – (of leaves) divided into a number of leaflets.
Cordate – heart-shaped at the base.
Corolla – the collective term for the petals.
Cultivar – plant variety created by cultivation.
Deciduous – plant whose leaves fall in autumn.
Dentate – toothed.
Dioecious – having male and female flowers on separate plants.
Drupe – succulent or spongy fruit, usually with a hard-coated single seed.
Entire – (of leaves) with an untoothed margin.
Fruits – the seeds of a plant and their associated structures.
Glabrous – lacking hairs.
Globose – spherical or globular.
Hybrid – plant derived from the cross-fertilisation of two different species.
Inflorescence – the flowering structure in its entirety, including bracts.
Introduced – not native to the region.
Involucre – ring of bracts surrounding a flower or flowers.
Lanceolate – narrow and lance-shaped.
Leaflet – leaf-like segment or lobe of a leaf.
Lenticel – breathing pore on a fruit, shoot or trunk.
Linear – slender and parallel-sided.
Lobe – a division of a leaf.
Midrib – the central vein of a leaf.
Native – occurring naturally in the region and not known to have been introduced.
Oblong – (of leaves) with sides at least partly parallel.
Obtuse – (of leaves) blunt-tipped.
Opposite – (usually of leaves) arising in opposite pairs on the stem.
Oval – leaf shape.
Ovary – structure containing the ovules, or immature seeds.
Ovoid – egg-shaped.
Palmate – (of leaves) with finger-like lobes arising from the same point.
Pedicel – stalk of an individual flower.
Perianth – collective name for a flower’s petals and sepals.
Petals – inner segments of a flower, often colourful.
Petiole – leaf stalk.
Pinnate – (of leaves) with opposite pairs of leaflets and a terminal one.
Pod – elongated fruit, often almost cylindrical, seen in pea family members.
Pollen – tiny grains that contain male sex cells, produced by a flower’s anthers.
Pubescent – with soft, downy hairs.
Rachis – main stalk of a compound leaf or stem of an inflorescence or array of fruits.
Reflexed – bent back at an angle of more than 90 degrees.
Sepal – outer, usually less colourful, segments of a flower.
Stamen – male part of the flower, comprising anther and filament.
Stigma – receptive surface of the female part of a flower, to which pollen adheres.
Style – an element of the female part of the flower, sitting on the ovary and supporting the stigma.
Tepal – perianth segment when petals and sepals are not identifiably separable.
Tomentose – covered in cottony hairs.
Whorl – several leaves or branches arising from the same point on a stem.
In many ways, trees and shrubs are no different from other flowering plants – they just happen to be bigger. They all grow, produce leaves, flowers and fruits in order to reproduce, and compete with other forms of life in the struggle to survive. The following is a basic review of the biology of trees and shrubs, which will help any reader unfamiliar with the subject to gain a better understanding of these fascinating organisms.
WOODY TISSUE
The principal way in which a tree or shrub differs from other, herbaceous, members of its family is its ability to produce woody tissue; this serves to conduct materials around the plant, and leads to the production of permanent shoots. In the case of perennial herbaceous plants, the shoots die back at the end of each growing season, or in the case of annuals, the whole plant dies and a new generation arises from seeds formed by the previous generation.
Trees and shrubs have an important layer of cells enclosing shoots, buds and roots, called the cambium layer. This is an active layer that is constantly producing new cells on its inner and outer surfaces. Cells that grow on the inside of the cambium develop into woody tissue or xylem; this conducts water from the roots to the shoots, buds and leaves. Eventually it forms the bulk of the trunk and branches of the tree as a new layer is laid down each year. Cells that grow on the outside of the cambium form the conductive tissue, known as phloem, that carries sugars from the leaves down to the roots. This vital layer must not be damaged. If a complete ring of this tissue is cut away from the trunk of a tree the roots will be deprived of nourishment from the leaves and the tree will eventually die.
A cross section through a Pedunculate Oak trunk reveals its many layers.
ANNUAL RINGS
When the tree begins to grow vigorously in the spring it forms large conductive cells that allow sap to flow freely through the trunk. As the season advances, cells produced by the cambium layer become smaller, with thicker walls for support, so they give a more dense appearance. In winter, cell production slows down and then ceases for a while; come the spring, however, there is a sudden burst of cell production and large cells are produced once more. The new growth of large cells immediately next to the thinner layer of dense cells gives the appearance of a ring. By examining a cut stump it is possible to count the rings and therefore discover the age of the tree, and also to find out which were the best growing seasons (see pp.).