Types of Tissues PDF

TYPES OF TISSUES - A tissue can be defined as a group of cells with a common origin. According to structure, tissues can be classified into: a-simple (homogenous) which consists of only one type of cells. b-complex (heterogeneous) which consist...

TYPES OF TISSUES - A tissue can be defined as a group of cells with a common origin. According to structure, tissues can be classified into: a-simple (homogenous) which consists of only one type of cells. b-complex (heterogeneous) which consists of more than one type of cells (as xylem, phloem, epidermis and periderm). - According to function, tissues cane be classified into: a-meristematic living tissues have the ability to divide and formation of new cells. b-permanent living and nonliving tissues formed with certain structure to perform certain function. Apical meristem of the stem (Promeristem) Ground Meristem Procambium Protoderm Primary Xylem Primary Phloem Vascular Cambium Ground Tissue (cortex & pith) Epidremis Secondary axylem Vascular Cambium Secondary phloem Ground Tissue (cortex and pith) Periderm Vascular Cambium 1  Promeristem Leaf primordium Dermatogen (protoderm) Zone of 1ry meristematic tissues Procambium Ground meristem Bud primordium 1ry phloem Vascular cambium Zone of 1ry ry 1 xylem Permanent tissues Epidermis Cortex Ground tissue Pith Leaf trace Leaf gab Periderm Zone of 2ry permenant tissues 2ry phloem 2ry xyle A LONGITUDINAL SECTION IN A DICOTYLEDONOUS STEM 2  Vascular Cambium Vascular cambium is the meristem that produces the secondary vascular tissues. It is a lateral meristem, the cells of which are highly vacuolated unlike most other meristematic cells. It is made up of two kinds of cells; the fusiform initials and ray initials. These two types of cells differ basically in size, shape and the fate of their products. The fusiform initials are relatively longer, spindle-like and produce the axial system of the secondary vascular tissues. The ray initials are almost isodiametric and their products differentiate as parenchymatous rays (horizontal system of the secondary vascular tissues). Fusiform initials Ray initials The cambial zone, thus, constitute a wide stratum of periclinally dividing cells organized into axial and ray systems. In the median plane of this stratum, there is a single layer of cambial initials. 3  The vascular cambium may be storied (stratified) or nonstoried (nonstratified). In the storied cambium, the fusiform initials divide transversely, there for, they are arranged in regular rows; while the fusiform initials in the nonstoried cambium divide obliquely, there for, have overlapping ends. The arrangement of the cambial initials determines the organization of the secondary vascular tissues. Cambial cell divisions Periclinal division producing one secondary vascular cell (xylem or phloem) and one cambial cell Vascular cambium To the Epidermis Anticlinal division producing two cambial cells (increasing the diameter) 4  The ray initials divide periclinally leading to the formation of radial files of cells (ray parenchyma) toward outside in the secondary phloem and inside in the secondary xylem.The ray initials also divide anticlinally in plants that have biseriate or multiseriate rays. Phloem fibers Secondary phloem Vascular Rays Vascular cambium (ray parenchyma) Secondary xylem Multiseriate ray initials Uniseriate ray initials Biseriate ray initials 5