The science of the structure of the organized plant body learned by dissection is called Plant Anatomy (anatomy- dissection). In general, Plant Anatomy refers to study of internal morphology, pertaining to different tissues. The subject of this chapter is structure of Angiosperms, with emphasis on primary tissues. Plant body in Angiosperms is differentiated into root stem, leaf and flower. All these parts are made up of different types of tissues containing different cell types. A tissue is a mass of similar or dissimilar cells performing a common function. The body of a vascular plant is composed of dermal tissue, Ground tissue and Vascular tissue. TISSUE TYPES:In broad sense, tissues are classified as – meristematic and permanent tissues.
Initially all embryonic cells of an embryo have the capacity to divide and multiply but as the embryo develops into a plant body, this capacity for division is restricted to certain parts of the plant body called meristems which are active throughout the life of the plant body (unlike that of an animal body). When meristematic cells divide, a group of the daughter cells remain meristematic; the other daughter cells called derivatives differentiate into various tissue elements. Before the occurrence of any cell division, usually cells become enlarged accompanied with addition of protoplasmic and cell wall material. Meristematic cells are isodiametric, compactly arranged with dense cytoplasm, large nucleus, and small vacuoles or without vacuoles. Cell walls are thin. Meristems which occur at the apices of stem, root and other branches are called apical meristems, which bring about primary growth of the plants, hence also called as primary meristems. In many plants in addition to apical meristems, lateral meristems like vascular cambium, cork cambium, intercalary meristems are found. Lateral meristems are arranged parallel to the sides of organs in which they occur.
Permanent or Mature Tissue:
Cells derived from meristems gradually change in their structure, metabolism and chemistry and acquire specialized characters by their various modes of differentiation. Not all the cells totally differ from the meristems. Some cells retain the power of division and others cannot divide. In a strict sense only cells which have lost the power for division must be regarded as permanent tissues, but in a broad sense, cells derived from meristem that have acquired a special function like photosynthesis, secretion, storage are treated as part of matured tissue. There are different types of mature tissues. Example: Parenchyma, Collenchyma, Sclerenchyma, Xylem and Phloem.