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Stem Structure
- 1. SUDIP SAMANTA MAHISHADAL RAJ COLLEGE B.SC HONOURS STUDENT
- 2. Primary Growth- Apical meristem Increases in length Secondary growth Lateral meristem Increases in grith or thickness
- 3. Vascular Bundles: Conjoint Collateral Open Cross sectional plan diagram of dicot stem
- 4. VASCULAR CAMBIUM INTRAFASCICULAR INTERFASCICULAR PERIDERM CORK CAMBIUM (PHELLOGEN) PHELLEM(CORK CELLS) PHELLODERM
- 5. Formation of cambium ring Origin of Secondary Tissues Formation of Annual ring Formation of Periderm GROWTH IN INTRASTELAR REGION GROWTH IN EXTRASTELAR REGION
- 6. Formation of cambium ring Formation of cambium ring INTRAFASCICULAR CAMBIUM + INTERFASCICULAR CAMBIUM
- 7. Origin of Secondary Tissues Secondary Xylem inner side of the cambium ring Secondary Phloem outer side of the cambium ring Secondary Medullary pass through the secondary xylem and phloem
- 8. Formation of Annual ring Spring wood or early wood. Autumn wood or late wood. Sapwood or alburnum Heartwood or duramen. Sap wood Heart wood
- 9. Formation of Periderm Phellogen or cork cambium . Phellem or cork Phelloderm
Editor's Notes
- Good morning everyone. Thank you for having me. My name is sudip samanta and I am going to be speaking to you today about secondary growth is dicot stem.
- This is my first slide At first I want to speak about the basic concept of secondary growth. Before that you need to know what is primary growth After that you can easily understand what is secondary growth. Ok first of all what is primary growth? Primary growth is a type of growth that occurs at the tips of root and shoots. Produced by cell divisions in the apical meristem. as a result of primary growth Increases in length of stem and root. And now I focus on secondary growth A type of growth that occurs distant from the apices as a result of increase in grith or thickness of stem or root through the formation of secondary vascular tissues and other tissues by the activities of lateral meristems like vascular cambium and phellogen(corck cambium) is referred to as secondary growth. Just in one sentence I say Primary growth means increases in length of stem and root. And secondary growth means increases in grith or thickness of stem and root. Secondary growth is noticed in gymnosperms, woody and herbaceous dicotyledons , and also in some monocotyledons.
- In this slide you see the diagrammatic view of dicot stem Outermost epidermis Thaen cortical layer ……….cortex is fully differenceated into three different layers which are 1) hypodermis 2) general cortex 3) endodermis ……….then the pericycle. In side the pericycle vascular bundle is present and centere pith is present , Now focous on vascular bundles. Conjoint means xylem and phloem on same radiis Collateral means xylem and phloem are arranged sid by side on same radius, xylem is seen towards the inner side and phollem towards outer side. Open means when cambium is present between xylem and phloem.
- Come to the 3rd slide The tissue involved in Secondary growth is CAMBIUM. So you can must say cambium is the king or master of secondary growth. Cambium is a meristematic tissue compossed of uniseriate layer or several layers living cells which are active sate of division. In plants primary vascular bundles are formed the cells of procambium strands to form xylem and phloem, where normal secondary growth takes place procambium strand remains meristematic and gives rise to proper cambium. There are several kinds of cambium found in plants stem and root. Vascular or Fascicular cambium:- This type of cambium is present in the vascular bundle. Intrafascicular cambium:- This tpyes cambium is present between the xylem and phloem of the vascular bundle. Interfascicular cambium:- During the secondary growth , intrafascicular cambium and medullary ray become meristametic and form some fragment ot strip those are called interfascicular cambium. Phellogen or Cork cambium:- Phellogen is present in extrastelar region (divided of cortex cell at the time of secondary growth). Phellogen consists of one type of cell. In LS section cells look rectangular or polygonal. They formed phellem and phelloderm. Phellem , phellogen and phelloderm- these three tissues are together known as periderm.
- Come to the next slide In stem, secondary growth in thickness is confined both in the intrastelar(within the stele) and in the extrastelar (outside the stele;in the cortex) regions. The event of intrasteler region is …………… The event of extrastelar region is …………...
- Come to the next slide a) Formation of Cambium ring:-. The cambium of the vascular bundle is called fascicular cambium.some of the living parenchyma cells of the medullary rays, mostly in the line with the fasicular cambium, become meristematic and form new strips of meristems known as interfascicular cambium-these two types of cambium i.e. fascicular and interfascicular cambium join with each other to form a complete and continuous ring known as cambium ring.
- the cambium ring becomes actively meristematic and formed new cells both externally and internally. New cells cut off on the outerside of the cambium ring are gradually converted into phloem elements-these phloem elements constitute the secondary phloem . The cells cut off on the inner side of the cambium ring are gradually converted into xylem elements thiese xylem elements constitute secondary xylem. It is to be noted that the cambium ring is more active on the inner side than the outer side as a result, large amount of secondary xylem is formed than phloem which very soon forms a compact mass. The cambium also produces short strips of parenchyma cells in radial directions which pass through the secondary xylem and the secondary phloem these strips of parenchyma are called secondary medullary rays or secondary rays.
- Formation of Annual rings, growth rings or growth layers takes place by the seasonal activity of the cambium. Cambium is more active in spring season during this season cambium producing greater amount of xylem vessels, this types of xylem or wood is called spring wood or early wood. Cambium is less active in winter season during this season cambium producing smaller amount of xylem vessels , this types of xylem or wood is called autumn wood or late wood. In a transverse section of the stem, these two types of wood appear together as a concentric ring known as annual ring or growth ring. The recently formed outer zone of such secondary xylem containing living cells that are still functional in condition and storage is called sapwood or alburnum. The earlier formed centrally situated xylem whose cells become non-functional in condition and storage is called heartwood or duramen.
- Periderm consists of three layers of tissues, viz. Phellogen or cork cambium Phellem or cork Phelloderm Phellem, phellogen, and phelloderm-these three together constitute a new secondary tissue in the cortex and are known as periderm. Origin of periderm:- In woody plants, cork cambium is the outermost lateral meristem. Cork cambium, also called phellogen, is another meristematic tissue developed in the cortex region. Due to the cambial ring activity, the outer layers such as cortex cells and epidermis get crushed. This is the time when the cork cambium develops as a new protective layer. This cork-cambium by meristematic activity cuts off new cells on both sides forming the secondary cortex or phelloderm on the inner side and cork on the outer side.
- This is time for questions and answer . If you have any query about my topic tell me……I will try to solve your query. Ok I thing you have no query
- Thank you so much everyone for listening to me . Have a nice day.