Plant Morphology 12/2/2017 1

Content Morphology and microscopy of the root Morphology and microscopy of the stem Morphology and microscopy of the leaf Morphology and microscopy of the flower Morphology and microscopy of the fruit Morphology and microscopy of the seed 12/2/2017 2

Morphology of the Root 3 Introduction Embryo develops into adult plant with roots, stem and leaves This is due to activity of the apical meristem A mature plant has three kinds of tissue systems 12/2/2017

Introduction cont… The dermal system includes the epidermis, which is the primary outer protective covering of the plant body 12/2/2017 4

Introduction cont… Fundamental (ground) tissue system form the ground substance of the plant in which other permanent tissues are embedded Parenchyma, collenchyma and sclerenchyma are the main ground tissues The vascular system contains two conducting tissues Phloem and Xylem 12/2/2017 5

Introduction cont… In different parts of the plants, the various tissues are distributed in characteristic patterns This is best understood by studying their internal structure by cutting sections (transverse or longitudinal or both) of the part (s) to be studied 12/2/2017 6

The Roots 7 Functions : – Support (anchorage), absorption, storage – Other functions? Types – Fibrous roots (1) Mat of thin roots that spread out Monocots – Tap roots (2) One large vertical root Also produces many small lateral, or branch roots Dicots Root hairs (3) Increase absorptive surface area /2/2017

Root: External Structures 12/2/2017 8

Root: Internal Structures 12/2/2017 9

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The Monocot Root 11 Internal structure of monocot roots shows the following tissue systems, from the periphery to the centre: Epiblema or rhizodermis, Cortex & Stele 12/2/2017

Root Structure: Monocot 12 Rhizodermis 12/2/2017

The Rhizodermis or Epiblema 13 Outermost layer of the root Single row of parenchyma cells, no intercellular space Stomata and cuticle are absent Root hairs are always unicellular Main function of rhizodermis Protection of the inner tissues of the root 12/2/2017

The Cortex 14 The cortex is made of only one type of tissue (parenchyma) Has many layers of parenchyma cells with lot of intercellular spaces Cortical cells are generally oval or rounded in shape; chloroplasts are absent The cells are living and possess leucoplasts The inner most layer of the cortex is endodermis and is composed of single layer of barrel shaped parenchymatous cells The function of cortical cells is storage 12/2/2017

Cortex cont… Endodermis (innermost layer of cortex) forms a complete ring around the stele (tissues inside endodermis) There is a band-like structure made of(thickened with) suberin present in the radial and transverse walls of the endodermal cells The band is called Casparian strip, after Casparay who first noted the strip The endodermal cells opposite to the protoxylem elements, are thin-walled without Casparian strips 12/2/

Cortex cont… These cells are called passage cells & their function is to transport water and dissolved salts from the cortex to the xylem Water cannot pass through other endodermal cells due to Casparian strips (blocking effect) The main function of Casparian strips in the endodermal cells is to prevent the re-entry of water into the cortex once water enters the xylem tissue 12/2/

17 T.S. of Maize root 12/2/2017

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Vascular System (Stele) 19 Vascular tissues are in radial arrangement with many protoxylem groups This arrangement of xylem is called polyarch and the xylem is in exarch condition The tissue present between the xylem and the phloem, is called conjunctive tissue 12/2/2017

The Pith 20 The central portion It consists of thin walled parenchyma cells with intercellular spaces These cells are filled with abundant starch grains 12/2/2017

The Dicot Root 21 xylemphloem Rhizodermis 12/2/2017

Rhizodermis or Epiblema 22 Outermost layer aka rhizodermis (epidermis in stems) made of a single layer of parenchyma cells which are arranged compactly without intercellular spaces Is devoid of stomata and cuticle Root hair is always single celled; Function(s)? The main function of rhizodermis is protection of inner tissues of the root 12/2/2017

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The Cortex 24 Consists of only parenchyma cells loosely arranged with intercellular spaces to make gaseous exchange easier These cells may store food reserves The cells are oval or rounded in shape Sometimes are polygonal due to mutual pressure Cortical cells are devoid of chloroplasts but starch grains are stored in them The cortical cells also possess leucoplasts 12/2/2017

Cortex cont… Inner most layer of the cortex is endodermis Endodermis is made up of single layer of barrel shaped parenchymatous cells Stele is completely surrounded by the endodermis The radial and the inner tangential walls of endodermal cells are thickened with suberin Casparian strips 12/2/

Cortex cont… Casparian strips are absent in the endodermal cells located opposite to the protoxylem elements These thin-walled cells without Casparian strips are called passage cells through which water and mineral salts are conducted from the cortex to the xylem elements Water cannot pass through other endodermal cells due to the presence of Casparian thickenings 12/2/

The Stele 27 Include all the tissues present inside endodermis The stele includes Pericycle and Vascular tissues 12/2/2017

The Pericycle 28 Pericycle is generally a single layer of parenchymatous cells found inner to the endodermis It is the outermost layer of the stele Lateral roots originate from the pericycle Thus, the lateral roots are endogenous in origin 12/2/2017

The Vascular Tissues 29 Vascular tissues are in radial arrangement Xylem and phloem are separated by a conjunctive tissue If conjunctive tissue is composed of parenchymatous tissue then, the xylem is in exarch condition If number of protoxylem points is four, then, the xylem is called tetrarch Each phloem patch consists of sieve tubes, companion cells and phloem parenchyma Metaxylem vessels are generally polygonal in shape but in monocot roots they are circular 12/2/2017

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