Horticulture Plant In Organization

A multicellular organism such as the plant, which carries out many complex processes involved in its growth and development, requires a complex organization to carry out its functions. To be efficient, the plant's structural unit must be sub-divided so that each major function is carried out by a particular area in the plant, i.e. an organ. The individual units of the plant, the cells, are grouped together into tissues of similar cell types, and each tissue contributes to the activities of the whole organ.

PLANT FORM

Most plant species at first sight appear very similar, since all four organs, the root, stem, leaf, and flower, are present in approximately the same form and have the same major functions.

In many species the functions of the root system are to take up water and minerals from the growing medium, and to anchor the plant in the growing medium. Two types of root system are produced; a tap root is a single large root which usually maintains a direction of growth in response to gravity (see geotropism), with many small lateral roots growing from it, e.g. in chrysanthemums, brassicas, dock; a fibrous root system consists of many roots growing out from the base of the stem, as in grasses and groundsel (see page 23 for root structure).

The leaf, consisting of the leaf blade (lamina) and stalk (petiole), carries out photosynthesis, its shape and arrangement on the stem depending on the water and light energy supply in the species' habitat (see page 31 for leaf structure).

The stem's function is physically to support the leaves and the flowers, and to transport water, minerals and food between roots, leaves and flowers. The leaf joins the stem at the node and has in its angle (axil) with the stem an axillary bud, which may grow out to produce a lateral shoot. The distance between one node and the next is termed the internode .Sexual reproduction is carried out in the flower, and therefore its appearance depends principally on the agents of pollination.

Adaptations to habitats such as deserts and forests can be seen in some species such that their organs have evolved to most efficiently survive that environment. Plants adapted to dry areas (xerophytes), e.g. cacti, have leaves reduced to protective spines and stems capable of photosynthesis. Some plants possess leaves modified for climbing in the form of tendrils, as in many members of the Leguminosae family, and Clematis climb by means of a sensitive, elongated leaf stalk. In runner beans and honeysuckle (Lonicera), twining stems wind around other uprights for support. Prickles are specialized outgrowths of the stem which assist the plant in scrambling over other vegetation, as in wild roses, while thorns may have a protective function, e.g. hawthorn (Crataegus). Some insectivorous plants