Oct 172012
 

The term ‘taxonomy’ was introduced by De Candolle in the year 1813 A.D. through his “Theorie Elementarie de la Botanique”. Taxonomy can be defined as a functional science which is guided by principles that have developed with the increase in knowledge of the plants. The first scientist was Carolous Linnaeus who formulated certain principles of taxonomy in his book Critica Botanica in the year 1737 A.D. Others were Adanson (1727 A.D.-1806 A.D.); De Candolle (1778 A.D.-1841 A.D.), John Lindley (1799 A.D.-1865 A.D.) and Sir Joseph Dalton Hooker (1817 A.D.-1912 A.D.). The phylogenetic systems of Bessey (1915 A.D.) and Hutchinson (1926 A.D.) are based on modern principles.

Taxonomy as a descriptive science started mainly with the works of Tournefort (1665 A.D.-1708 A.D.), De Jussieu (1699 A.D.-1771 A.D.), Carolous Linnaeus (1707 A.D.-1778 A.D.). Most of the taxonomic works of this period were based on the observations of the similarities and dissimilarities of gross morphological characters of the plants. Plants were described and classified on the basis of these characters. With the progress in research and added knowledge, taxonomists classify the plants in such a way that give us an idea about the sequence of their evolution from simpler, earlier and more primitive types to complex, recent and more advanced types.

The system of classification proposed by Takhtajan in 1967 A.D. is mainly based on modern principles such as evolutionary sequence, genetic relationships, fossil records, morphological, cytological, physiological, anatomical, embryological, biochemistry and pollen grain characters. While developing a system of classification, the general basic principles taken into consideration are given below:

  1. Morphological Criteria: Ever since the beginning, morphological characters of plants were taken into consideration at the time of classification. Earlier artificial systems were based on only one or a few morphological characters. Even today, the fact cannot be denied that morphological characters have their own importance in taxonomy and all systems of classifications suggested are based on the principles of morphology. Some of the vegetative characters such as annual, biennial and perennial duration of plants, kinds of root, nature of the stem, leaf arrangement, leaf venation, presence and absence of stipules are taken into consideration. But more emphasis is laid on the floral characters because they are less affected by the change in environment. The common floral characters are presence and absence of calyx and corolla, aestivation of calyx and corolla, fused or free condition of corolla, number, arrangement and fusion of androecium and gynoecium, ovary with its placentation etc.
  2. Anatomical Criteria: Anatomical characters such as arrangement of vascular bundles, orientation of xylem and phloem in the bundles, nature and origin of secondary tissue and leaf trace development are used in solving taxonomic problems. These criteria are taken into consideration for the categorization in classification. It is observed that the same group of plants show close relation between the morphological characters and anatomical structures. For example, the arrangement of vascular bundle in a ring is common among the dicot and scattered vascular bundle among the monocot.
  3. Phylogenetic Criteria: The modern system of classification is mainly based on the phylogenetic criteria. Phylogeny may be defined as the study of the evolutionary sequences or history of organisms in different periods of the earth’s history. These systems also reflect on the genetic relationships of the plants. Engler and Prantl (1887 A.D.-1899 A.D.), system of classification can be considered as first phylogenetic system of classification. Others are Bessey, Hutchinson, Cronquist and Takhtajan.
  4. Palaeobotanical Criteria: Palaeobotany is the study of fossil plants. Critical examination of fossil plants help to solve taxonomic problems as well as it gives clear idea about the evolutionary relationship. Thus, palaeobotany made phylogenetic basis for classification.
  5. Cytotaxonomy: It is the utilization of cytological characters for the elucidation of taxonomic problems. Cytological characters such as chromosome number, shape, size and behavior during cell division are used in solving taxonomic problems.
  6. Chemotaxonomy: Chemotaxonomy or chemical taxonomy is defined as the application of chemical data in solving taxonomic problems. The presence and distribution of various chemical compounds in plants serve as taxonomic evidences. Although, several chemical compounds are found in plant body, only thirty three different groups of chemical compounds provide valuable taxonomic clues.
  7. Numerical Taxonomy: Numerical taxonomy can be defined as the grouping of taxonomic units by the application of numerical methods (data). In the classification of flowering plants, numerical taxonomy was at first introduced by Edger Anderson (1949 A.D.). The main objective of numerical taxonomy is to clarify and illustrate degrees of relationship or similarity in an objective and repeatable manner. High speed computers are used for this purpose.
Sep 102012
 


Biology is one of the most important branches of science. It is a science that deals with living things. In other words, biology is the study of life. The word ‘Biology’ is derived from two Greek words: Bios meaning life and logos meaning the discourse or study. Life exists in two forms i.e., plants and animals.

There are two main branches of biology. They are Botany and Zoology. Botany is the branch of biology that deals with the study of plants whereas Zoology is the branch of biology that deals with the study of animals. These two main branches of biology can further be divided into several other branches which deal with the different aspects of plant and animal science. Some of those branches are given below:

1. Morphology (Greek: Morphe-form, logos-study): The study of external form and structure of living organisms is called morphology.

2. Anatomy: The study of internal structure of plants and animals is termed as anatomy.

3. Histology: The study of details of tissue structure of organisms is called histology.

4. Cell Biology: The study of structure, functions, reproduction and life history of cells is called cell biology.

5. Molecular Biology: The study of physio-chemical organization of biomolecules called molecular biology.

6. Physiology: The study of processes and functions associated with life is called physiology.

7. Genetics: The study of heredity and variations is called genetics.

8. Embryology: The study of early stages of development, such as gametes formation, fertilization of eggs and development of the embryo is called embryology.

9. Taxonomy: Taxonomy is that branch of science which deals with the identification, nomenclature and classification of biological objects.

10. Palaeobiology: The study of fossil plants and animals is called palaeobiology.

11. Economic Biology: The study of economically important organisms and their products is called economic biology.

12. Ecology (Greek: oikos-house or habitat, logos-study): The study of plants and animals in reciprocal relationship with the environment is called ecology.

13. Evolution: The change in living organisms over time and adaptation to the conditions of their environment is called evolution.

14. Microbiology: The study of microorganisms such as bacteria, is known as microbiology.

15. Protozoology: The study of unicellular organisms is called protozoology.

16. Mycology: The study of fungi is called mycology.

17. Phycology: The study of algae is called phycology.

18. Bryology: The study of liverworts and mosses is called bryology.

19. Helminthology: The study of worms is called helmithology.

20. Parasitology: The study of parasitic organisms is called parasitology.

21. Entomology: The study of insects is called entomology.

22. Ornithology: The study of birds is called ornithology.

23. Mammalogy: Mammalogy is the study of mammals.

24. Herpetology: Herpetology is the study of reptiles and amphibians.

25. Limnology: The study of fresh water and its inhabitants is called limnology.

26. Biometrics: Biometrics is the study of mathematical statistics in relation to biological research.

27. Surgery: It is a branch of medicine which involves physical operation to cure diseases or injuries to the body.

28. Psychology: The study of human behaviour and mental quality is known as psychology.

29. Palaeontology: The study of extinct and fossil organisms is called palaeontology.

30. Veterinary: The study of the diseases of domestic animals and their treatment and health care is called veterinary.

31. Anthropology: The study of origin, physical and mental development of mankind in the present and past races with social conditions is known as anthropology.

32. Biochemistry: The study of chemical substances and chemical processes of living things is known as biochemistry.

33. Biophysics: The application of physics to the study of living things is called biophysics.

34. Exobiology: The study of the existence of life in other planets is called exobiology.