Jain Biology ► [01] Biology : Science Of Living Organisms ► 4. Flower

Posted: 11.09.2009

An individual flower consists of groups of modified and highly specialized leaves arranged concentrically, designed specially for the purpose of reproduction. These groups of modified leaves are:

  1. sepals which protect the delicate stamens and pistils when the flower is in the bud stage;
  2. petals which attract pollinating insects;
  3. stamen which consists of a stalk and a pollen sac called an anther which produces pollen which in due course contains pollen grains (For this reason the stamens are called male sex organs of the plant);
  4. pistil which consists of an ovary, style and stigma; the ovary produces one or more ovules which in due course contains, with other cells an egg. (For this reason the pistil is called the female sex organ of the plant).

A plant develops flowers after it has attained maturity in its vegetative parts. It has two parts, the pedicel or the stalk and the thalamus or the swollen tip with the floral parts.
Many flowers possess bright colours, perfume and nectar (sugary liquid) to attract insects for pollination.

Gynaecium or Pistil is the female reproductive whorl which is made up of three parts, stigma, style and ovary. The stigma receive the pollen grains; the style is the tubular stalk which connects stigma to the ovary which is the swollen basal part formed by the union of one or more carpels which are formed like chambers. A pistil may have only one carpel or two or more. Within each carpel are seen one or many ovules, each arising along the projection called placenta. The ovule attaches to the placenta by a short stalk. In the ovule is an embryo sac with an egg or the female gamete. During fertilization, one of the male gametes from the pollen fuses with the egg.

The flowers which contain all four of the main parts are called complete flowers while others are called incomplete flowers.

One of the most conspicuous features of the plant kingdom to the layman and botanist alike is the infinite variety of size, form, and behaviour of its members. Plants vary in size from structurally simple, microscopic organisms such as bacteria, some of which are only 1/2 micron long by 1/5 micron wide to seaweeds which may be several hundred feet long, and California redwoods, some of which attain heights of over 350 feet, diameters of 30 feet and weights of 2100 tons (these redwoods are the tallest known land plants). In most cases, each species has a characteristic average size range, but plants are exceedingly susceptible to environmental conditions and individuals are often larger or smaller, depending upon the nature of surroundings in which they have grown.

The forms of plants vary even more than do their sizes. As we shall presently see, there are 340,000 distinct species with numerous varieties. Each species has its own characteristic habit of growth, shape of leaves, method of branching, form, and colour of reproductive structures and other peculiarities which give it a personality of its own. Some plants are trees, others are woody vines, some are herbaceous (soft-stemmed) vines, still others are erect herbs. Some have large leaves, some have small leaves, some have leaves with toothed or otherwise indented margins, while some are with smooth margins. Some have no leaves but consist entirely of stems, roots, and flowers; others have simple bodies not differentiated into roots, stems, leaves or flowers.

Some plants (desert plants for example) grow very slowly, so slowly that any increase in heir size is noticeable only it.hey are examined at intervals of several years. In tropics, however, growth frequently proceeds at incredibly rapid rates. These are extremes, All given plants manufacture sugar by the process of photosynthesis, but they utilise this sugar in different ways. Some convert them into fatty substances which they store in their tissues; others transform them into starches as storage of foods. Some plants elaborate large quantities of organic acids—citric acid in lemons and oxalic acid in rhubarbs. Some manufacture aromatic oils—dill, caraway, spearmint, sassafras, lavender, peppermint etc.

Another physiological difference among plants is found in their longevity. Bacteria live for 20 or 30 minutes and form two new organisms, which in turn form offspring of their own. At the other extremes of age are certain coniferous trees, such as California redwoods which attain ages over 3000 years. Many wild and cultivated plants are annuals, which live but a singlegrowing season, some are biennials, which live through two seasons and others are perennials which continue to grow for man) years. Trees and shrubs are perennials.

Plants vary, moreover, in their methods of reproduction and in the structure and development of their reproductive organs. Plants are classified in groups to indicate something of their evolutionary positions and their mutual relationships. Reproductive organs and processes, being more stable than roots, stems and leaves, they are the principal criteria of systematic arrangement. Earlier attempts at classification were largely artificial. The more nearly natural systems have grown mainly within the last century.

The, most nearly natural system of classification is the division of the plant kingdom into two subkingdoms- - "THALLOPHYTA", i.e., plants not forming embryos (algae, fungi) and "EMBRYOPHYTA" i.e., plants forming embryos (mosses to angiosperm). We shall deal with all these in detail in succeeding sections.

More than 340,000 species of plants have been identified under different conditions. The plant kingdom is divided into two groups;

  1. Cryptogams, lower plants without flower and seed
  2. Phanerogams, higher plants with flowers and seeds
  1. Cryptogams are divided into three divisions:
    1. Thailophyta—(thailes—a young shoots phytonplant).
      Simplest of all plants since plant body is not differentiated into root, stem and leaf and is called the thallus. They are divided into four group
      1. Bacteria, the simplest living organisms. They are unicellular and without chlorophyll.
      2. Algae possess chlorophyll and are able to manufacture their own food by photosynthesis.They mostly grow in water:
      3. Fungi lack chlorophyll hence they live as parasites. Fungi like penicillum and yeasts have been put to the benefit of mankind.
      4. Lichens are associations of an algae and a fungus living together, former preparing food while the latter absorbing water and minerals. They grow on tree trunks and other moist places.
    2. Bryophyta—they develop root like structures called rhozoids. Their life cycle shows alternation of generations;[1] the main plant is a gametophyte[2] on which the sporophyte[3] (asexual stage) grows as a dependent body, e.g. Mosses with the stem axis bearing leaves, [cf, plants growing on plants (vṛkṣayonika) in Sutrakṛitāṅga Sūtra].
    3. Pteridophyta (pteros=fern). The plant body is with roots stem and leaves, highest group of cryptogams. The main plant is a sporophyte while the gametophyte is very small.
  2. Phanerogams are the most advanced type of plants with flowers and seeds. They are divided into two sub-divisions:
    1. Gymnosperms (Bymno=naked, sperma=seed). They possess simple, unisexual flowers. The seeds are not enclosed in the fruit hence they are naked seeds e.g. pines
    2. Angiosperms (Gr. angion - case). They are the most highly advanced group of plants, commonly referred lo as dowering plants. The flowers are complex and the seeds are enclosed in the fruit. They are divided into two classes:
      1. Monocotyledons - the group with one colytedon in the embryo of the seed
      2. Dicotyledons - the group with two colytedons in the embryo of the seed

Monocotyledons are further divided into seven series, while Dicotyledons, being the larger group are divided into three subclasses each which is further divided into various series. Each of the series again divided into orders and the order into families and so on. In the flowering plants study of the family is considered most important.

Of t he 342,000 species of plants on record, the following is the rough distribution:

Thailophyta

-

110,000 species

Bryophyta

22,300 species

Pteridophyta

10,000 species

Gymnosperms

700 species

Monocotyledons

40,000 species

Dicotyledons

159,000 species

From the above, it is seen that angiosperms constitute, 199,000 i.e. 60% of total species of plants.

Footnotes:
[1]
[2]
[3]
Share this page on: