11th Class

The word “Meristem” originated from “Meristos” (Greek = continuous division) and the term meristem was introduced by Nageli (1858). A group of cells which are much active and capable of showing continuous divisions and redivisions, is called as meristematic tissue. The various characteristic features of the meristems are discussed below : (1) They contain immature and young cells and are capable of repeated divisions. (2) Intercellular spaces are not present in meristematic tissue. (3) They contain a homogeneous thin cellulosic wall. (4) They contain large nuclei associated with abundant cytoplasm. (5) They are metabolically very active but they do not store food material and further no plastids in them. (6) Vacuoles are small or absent. (7) Meristematic cells are isodiametric in shape. (8) Undifferentiated tissue in which cells divides continuously           Types of meristems The meristems may be classified on the more...

Permanent tissues are made up of mature cells which have lost the capacity to divide and have attained a permanent shape, size and function due to division and differentiation in meristematic tissues. The cells of these tissues are either living or dead, thin-walled or thick-walled. Permanent tissues are of following types : Simple permanent tissues Simple tissues are a group of cells which are all alike in origin, form and function. They are further grouped under three categories : (1) Parenchyma : Parenchyma is most simple and unspecialized tissue which is concerned mainly with the vegetative activities of the plant.     The main characteristics of parenchyma cells are : (i) The cells are living, thin walled, soft, possess a distinct nucleus, having well developed intercellular spaces, vacuolated cytoplasm and cellulosic cell wall. (ii) The shape may be oval, spherical, cylindrical, rectangular more...

The increase in thickness or girth due to the activity of the cambium and the cork cambium is known as secondary growth. (1) Secondary growth in stem : On the basis of the activities of cambium and cork-cambium, secondary growth in stem can be discussed under the following heads : Activity of cambium : The vascular cambium in between xylem and phloem is called intrafascicular or fascicular cambium which is primary in origin. At the time of secondary growth the parenchymatous cells of medullary rays between the vascular bundles become meristematic and form strip of cambium called as interfascicular cambium which is secondary in origin. Both inter and intrafascicular cambium joins together and form cambium ring which is partly primary and partly secondary in origin. By anticlinal divisions the circumference of the cambium increase. By periclinal division cambium produces the secondary xylem and phloem tissues on innerside and outerside. The more...

These tissue perform special function in plants, e.g., secretion of resins gum, oil and latex. These tissues are of two types : (1) Laticiferous tissues : They are made up of thin walled, elongated, branched and multinucleate (coenocytic) structures that contain colourless, milky or yellow coloured juice called latex. These occur irregularly distributed in the mass of parenchymatous cells. Latex is contained inside the laticiferous tissue which is of two types : (i) Latex cells : A laticiferous cell is a highly branched cell with long slender processes ramifying in all directions in the ground tissue of the organ. They do not fuse and do not form network. Plants having such tissues are called simple or non-articulated laticifers. e.g., Calotropis (Asclepiadaceae) Nerium, Vinca (Apocyanaceae), Euphorbia (Euphorbiaceae), Ficus (Moraceae). (ii) Latex vessels : They are formed due to fusion of cells and form network like structure in all directions. At maturity, more...

Several tissues may collectively perform the same function. A collection of tissues performing the same general function is known as a “Tissue System''. According to Sachs (1975) there are three major tissue systems in plants as follows : (1) Epidermal tissue system : The tissues of this system originate from the outermost layer of apical meristem. It forms the outermost covering of various plant organs which remains in direct contact with the environment. Epidermis : Epidermis is composed of single layer of cells. These cells vary in their shape and size and form a continuous layer interrupted by stomata. In some cases epidermis may be multilayered e.g. Ficus, Nerium, Peperomia, Begonia etc. The epidermal cells are living, parenchymatous, and compactly arranged without intercellular spaces. Certain epidermal cells of some plants or plant parts are differentiated into variety of cell types : (i) In aerial roots, the multiple epidermal cells are more...

It can be defined as modified dwarf shoot which is meant for sexual reproduction. It is characteristic feature of angiosperm. Parts of a typical flower : A typical flower of an angiosperm consists of four types of floral parts namely calyx, corolla, androecium and gynoecium. General description of a flower The flowers are termed pedicellate if they possess stalks and sessile if they lack them. The flower may be described as complete if it bears all the floral parts and incomplete, when one or more floral parts are absent. Flowers are called bisexual if they bear both androecium and gynoecium. The unisexual flowers have either androecium or gynoecium. The unisexual flowers may be male flowers or female flowers. The male flower are also called staminate flowers as they have stamens only. The female flowers have only the carpels and hence called pistillate flowers. Flowers with sterile sex organs are described more...

The flowers are arranged in some definite manner on the plant in each species of the flowering plants. The mode of arrangement of flowers on a specialised branch on top of the plant which bears flowers is called inflorescence. The stalk of the inflorescence is called peduncle. Depending upon the arrangement of flowers, inflorescence is classified as follows :