INTRODUCTION
Identification forms the basic requirement to know any substance including plants. The knowledge of action and benefits will only be useful when there is the correct ingredient used to prepare the formulation which may be either nutritional or medicinal. In case of a medicinal requirement, the responsibility will be much more on the person who does the formulation as there will be involvement of those materials which is not being used in common like the poisonous or high potency substances. Thus for proper identification, the knowledge of the macroscopic and microscopic structures is very beneficial. This holds good for every substance namely plants, minerals and animals. The part of science that deals with the same is known as Pharmacognosy. In general the definition of Pharmacognosy by American Society of Pharmacognosy states that “the study of the physical, chemical, biochemical, and biological properties of drugs, drug substances, or potential drugs or drug substances of natural origin as well as the search for new drugs from natural sources.”
The pharmacognosy study is conducted on the Macroscopic and Microscopic characters of the substance where their basic knowledge will aide in the majority of identification process if not precise. As the subject of Dravyaguna deals more with the plants, the present description will be regarding plants.
MACROSCOPIC CHARACTERS OF PLANTS
The macroscopic characters of the plants include all the different data regarding the shape, size, number, etc characters that can be seen through our naked eye. In general the plants are divided into 5 kingdoms namely Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms. The part that is discussed mainly with the purpose of identification are characters concerned to the vegetative and floral parts that are very crucial for identification of Flowering plants or Angiosperms as they are the majority of the flora that is being used in medicine. Among the two, the vegetative parts give a gross idea while the floral parts give a clear idea for the identification purpose. In fact it is the prime method used during the field identification of the plant present in its natural or cultivated habitat.
GENERAL FEATURE
Angiosperms are the plants that flower and have seeds that are enclosed in fruits and seed coats. The size of these plants vary considerably and can grow over 100 mts height. They are generally classified into two major groups namely Dicotyledons and Monocotyledons depending on the cotyledons in the seeds. But there are other features that differentiate is that Dicots have Reticulate venation, tap root system and tetramerous or pentamerous flowers (four or five floral whorls) while Monocots have Parallel venation, fibrous root system and trimerous flowers (three floral whorls) generally. But according to the different need and environment conditions, these plants undergo modifications which form the object of identification of the plant. Based on the sizes the plants are known as Herbs, Shrubs, Climbers or weak stemmed plants and Trees which is the most basic point of identification
ROOT
Roots form the part of the plant that go into the soil with some exceptions. They are developed from the radicle of the sapling. Basically roots are of three types namely Tap root, Adventitious root and Fibrous root. The tap root is made up of one main root system along with other branches or sub-branches. It is commonly seen in dicots. The adventitious roots are those which are developed from parts of the plant other than the radicle which may be branched or unbranched and are usually developed for certain purpose like storage of food, etc. Lastly, the fibrous roots are those where the radicle gets replaced by a large number of roots right from the base of the plant. It is commonly seen in monocots. These roots undergo modification sometimes for performing special functions like storage. To know more about the details of root morphological characters……………click here.
STEM
Stem form the the part of the plant that is above the soil. This is the part that develops from the plumule part of the sapling. Basically, it is differentiated by the presence of nodes and internodes. these nodes give rise to branches, leaves, flowers, bracts, stipules, etc. It supports conduction of water, minerals, photosynthesis, storage of food, vegetative propagation, protection, etc. The basic classification of plants as herbs, shrubs, trees and climbers was done on the basis of the characteristic features of the stem.
Herbs are those plants which have a soft, green and delicate stem. They are usually small in size and are devoid of any woody tissues. The size may vary from 6 inches to 6 feet tall, but many are around 2 to 3 feet in height. Shrubs are medium sized woody stemmed plants which grow taller than herbs but are shorter than trees. They are usually bushy in appearance and are of 6 to 10 feet in height. The trees are the tallest among the plants and have a thick, woody, strong stem known as trunk. The leaves and other parts of the plant are found on top of the trunk and is known as the canopy. Lastly the weak stemmed plants that are thin, long and need support to stand upright are known as climbers or creepers (that which creeps along the ground). To know more about the details of stem morphological characters ……………………..click here.
LEAVES
Leaves are the important part of the plant as they are the one which are responsible for the majority of the functions that take place in the plant. Right from the function of photosynthesis to respiration and all the necessary functions, leaves have their own levels of contributions. For the purpose of identification also these form a very important part. This is due to the fact that they are of different shapes, present different margins, lengths, and many other features that make them many a times unique and an important feature of identification. But still these are not considered to be standards for identification by the taxonomists due to the fact that they undergo a very considerable variation with respect to environment and the availability of the resources. But among the vegetative parts this is one of the most important part for identification. Even though we cannot assess the identity to the precise and pin point level, still it can give a very considerable idea of the genus and sometimes even the species of the plant.
This is possible by the help of the characters, features, patterns of venations, lengths, etc that differ form one plant to the other. But basically, leaves are of two types namely Simple leaf and Compound leaf. This characteristic feature itself differentiates number of families and gives a gross idea to which family the plant belongs. To know more about the details of leaf morphological characters and understand it more clearly ……………..click here.
INFLORESCENCE
Inflorescence is said for the arrangement of flowers in a particular manner or pattern on what is called as the floral axis. If the flowers are single then it would be usually considered as solitary but when there are many, then they are arranged in a particular pattern. The pattern of arrangement will give an idea regarding the different families too. Hence they form the important point of identification. Basically these inflorescence is mainly of three varieties namely Racemose, Cymose and Special or Unique. The Racemose and Cymose are the two commonly seen varieties while the Unique are usually seen in certain families which is an important observation from the identification point of view. To know more about the details of Inflorescence and understand it more clearly ………………click here.
FLOWERS
Flowers are the most important parts of the plant as they are the most stable parts with respect to the any changes in the environmental conditions. The floral data is considered to be the basic standard for the subject of taxonomy. Hence, it is an important part that is to be considered for the purpose of identifying the plants. Every character is identified and is the major method for differentiation between species and sometimes even the sub-species also. Other than this it is the reproductive part of the plant which on fertilization produce fruits and seeds. This will be important from the plant point of view as it continues the existence of the plant species. The part from where the flowers arise is known as the bracts. The flower stalk or the part with which it gets connected to the rest of the plant is known as pedicels where the upper part which is swollen is called the thalamus or the receptacle. The parts namely the sepal, petal, stamen and carpels are together known as Floral leaves. To know more about the details regarding the morphological characters of flower and understand it more clearly ………………….click here.
FRUITS
Fruits are the one that are part of the plant which is basically used to carry on the existence of the plant into the next generation. It is that part of the plant which possess the seeds and provide the basic protection and sometimes even the nutrition that can be used during the development of the seeds further to become the plant. But some fruits don’t have seeds in them which are known as Parthenocarpic or Seedless fruits. These fruits are of different shape, size, colours, etc. making it a point of observation for the purpose of identification. The characters of flowers and fruits are the main points that a taxonomist observes while classifying plants. Fruits are those which are resultant of the fertilization of flowers and is may be edible or non-edible. To know more about the details regarding teh morphological characters and other details of the fruit, then …………..click here.
MICROSCOPIC CHARACTERS OF PLANTS
The microscopic character is known by taking a part of the plant material and analysing it under a compound microscope. The section may be of transverse, longitudinal or any other way which is comfortable to get the best observational field under the microscope. The section is then suitably stained by using Leishmann’s stain or Methylene blue, etc which is suitable to the specimen under study and observed under the suitable lens.
GENERAL FEATURE
The microscopic characters are interpreted on the basis of cells, tissues and other structures or components. Among the three the most common aspect that is being studied in the pharmacognosy is the observation of cells and the tissues. Anyway the cell is a unit while the tissue is made up of cell groups. Thus a tissue is defined as a group of cells which have a common origin that may be of similar or dissimilar shapes but usually perform a common function. These tissues are divided broadly into two types namely the Meristematic Tissues and the Permanent Tissues.
MERISTEMATIC TISSUE
This tissue consists of undifferentiated, immature cells which are in a continuous state of cell division. They don’t have a secondary cell wall but have a primary wall made of cellulose. They have dense cytoplasm and a large nucleus and are without vacuoles. Since there is no intercellular spaces, the cells in this tissue is closely packed and is compact in structure. These cells are of three types depending on the development and origin namely Primary, secondary and Positional meristems
PRIMARY MERISTEM
These are the cells that are developed from the promeristem which is the basic cells of development and are present right from the embryonic stage. They are always undergo division and are the ones who form the Primary Permanent Tissue.
SECONDARY MERISTEM
When the meristematic tissue is developed from the Primary permanent tissues then they are known as secondary meristem. These are responsible for the secondary growth in plants.
POSITIONAL MERISTEM
The positional meristem is named or identified on the basis of their presence in certain regions of the plant namely Apical Meristem, Intercalary Meristem and Lateral meristem.
PERMANENT TISSUE
The permanent tissues are the those cells which have lost the power to divide and undergo any changes or differentiation. They may be either dead or living and are for useful in performing certain functions too. These are of three types namely Simple and Complex tissues.
SIMPLE PERMANENT TISSUES
These are homogenous tissues as they are made up of similar type of cells or only one variety of cell having a common functions. This is again classified into three types namely Parenchyma, Collenchyma and Sclerenchyma.
Parenchyma are the first set of secondary tissues to be derived from the meristems. Hence it is also known as the fundamental tissue. It is a thin-walled cell with a large central vacuole and is a common tissue with large intercellular spaces making it a loose tissue. This tissue mainly deals with the storage of food. The cells are usually spherical or polyhedral in shape.
Collenchyma is a mechanical tissue which is devoid of lignin. They are elongated with the localised deposition of pectin and hemicellulose. They are generally without and intercellular spaces but sometimes do have some cytoplasm along with large central Vacuole. Sometimes even the chloroplasts also can be seen in the region of the cytoplasm.
Lastly, Sclerenchyma which is a main mechanical tissue and is a long, narrow, thick-walled, lignified and dead tissue which has the primary function of providing the mechanical support to the plant.Due to the deposition of lignin on the walls of the cells, there is formation of pits. Eg. Sclereids
COMPLEX PERMANENT TISSUES
The complex permanent tissue are those which have more than one type of cells where they work together in synchronization as a unit. These tissues are heterogeneous in nature and have their origin from the procambium. These tissues are of two types namely Xylem and Phloem.
The xylem are the water and mineral salts conducting tissues and is composed of four elements namely Tracheids, Vessels or Tracheae, Xylem Fibres and Xylem Parenchyma. Here except Parenchyma all are dead tissues. The xylem is of two types based on origin namely Primary Xylem and Secondary xylem. The primary xylem is composed of Metaxylem and Protoxylem which take its origin from Procambium while the secondary xylem originates from vascular cambium.
The phloem are the food conducting tissues usually from leaves to other parts of the plant and is composed of Sieve cells or tubes, Companion cells, Phloem fibres and Phloem Parenchyma. Like Xylem even phloem is also of two types based on the origin namely Primary and Secondary Phloem. The primary phloem is composed of Metaphloem and Protophloem which take its origin from Procambium while the secondary phloem originates from vascular cambium.