are formed in secondary xylem vessels that have last their function i.e., in heart wood. compounds made during photosynthesis to various parts of plant. Some commercially important phloem or bast fibres are obtained from the following plants. i.
Flax- Linum usitatissimum ii. Hemp- Cannabis sativa iii. Sun hemp- Crotalaria juncea iv. Jute- Corchorus capsularis Be friendly with your environment (Eco friendly) Why should not we use the natural products which are made by plant fibres like rope, fancy bags, mobile pouch, mat and gunny bags etc., instead of using plastics or nylon?
Periderm Whenever stems and roots increase in thickness by secondary growth, the periderm, a protective tissue of secondary origin replaces the epidermis and often primary cortex. The periderm consists of phellem, phellogen, and phelloderm. Phellem (Cork) First cork cell Cuticle Epidermis Cortex Phellogen (Cork cambium) a b Phellem(Cork) Cuticle Epidermis Cortex Phellogen (Cork cambium) Phelloderm (Secondary cortex) Figure . : The cross section of periderm (a–b) It is the protective tissue composed of non- living cells with suberized walls and formed centrifugally (outward) by the phellogen (cork cambium) as part of the periderm.
It replaces the epidermis in older stems and roots of many seed plants. It is characterized by regularly Bark Sap wood Heart wood Annual rings Figure . : Cross - section of wood showing annual ring Differences Between Sap Wood (alburnum) and Heart Wood (duramen) Sap Wood (Alburnum) Heart Wood (Duramen) Living part of the wood. Dead part of the wood.
It is situated on the outer side of wood It is situated in the centre part of wood It is pale coloured It is dark coloured Very soft in nature Hard in nature Tyloses are absent Tyloses are present It is not durable and not resistant to microorganisms It is more durable and resists microorganisms Secondary Phloem The vascular cambial ring produces secondary phloem or bast on the outer side of the vascular bundle. Just as the secondary xylem, the secondary phloem also has two tissue systems – the axial (vertical) and the radial (horizontal) systems derived respectively from the