Anatomy is the study of internal structure of plants and their organs. Tissue is a group of cells of similar or dissimilar structure that perform a common function and all component cells have a common origin, There are three broad kinds of tissues: meristematic tissues, permanent tissue and secretory tissue.
Meristematic tissue is the group of cells having a continuous power of division, whereas meristem is the region containing meristematic cells. Cells of the meristematic tissues are compactly arranged, have no intercellular space; densely protoplasmic with a large nucleus, no ergastic substances and vacuoles; thin primary cell wall and are metabolically very active. Meristems may be primary or secondary depending on the origin or may be apical, intercalary or lateral depending on position. Apical and intercalary meristem help in longitudinal growth of plant and its branches whereas lateral meristem helps in the radial growth in matured parts.
Organisation of shoot apex has been explained by Apical cell theory (Nageli, 1868), Histogen theory (Hanstein, 1868) and Tunica-Corpus theory (Schmidt, 1924). Organisation of root apex is explained by Quiescent Centre Concept, Histogen theory, Korper and Kappe theory.
Permanent tissue is a group of cells which have temporarily or permanently lost the power to divide. Parenchyma, collenchyma and sclerenchyma are three types of simple permanent tissues as each of them contain similar cells. Parenchyma is called the fundamental tissue. Collenchyma is a living mechanical tissue and sclerenchyma is a nonliving mechanical tissue.
Xylem and phloem are two complex tissues and their components are different in structures. Xylem (wood) is composed of four elements: tracheid, vessels, parenchyma and wood fibre. Out of these only xylem parenchyma is living component. Xylem helps in conduction of water and minerals from roots to different parts. Xylem may be protoxylem or metaxylem; or primary and secondary in nature, or may have endarch, mesarch and exarch condition.
Phloem is a living tissue. It contains five elements: sieve cells, sieve tubes, phloem parenchyma, companion cells and bast fibres. Sieve tube cells are found only in angiosperms and are the largest cell in the plant. Phloem, like xylem, may be primary or secondary; or proto phloem or metaphloem. Phloem helps in conduction of organic solutes to different parts from the leaves.
Secretory tissue is a special tissue as it is considered as a group of cells performing a common function. Secretory tissues are mainly two types: glandular tissues and laticiferous tissue. Nectaries, trichomes, osmophors, digestive glands are external in nature where as some oil glands and hydathodes are internal in nature. Laticiferous tissue contains latex and are of two types: latex cells and latex vessels. They are multinucleated branched structures which spread amongst the permanent tissues. Contents of laticiferous tissue are of great economic Importance.