Tyloses (singular – tylosis) are the balloon like outgrowth of parenchymatous cells to the lumen of tracheids or vessels of the secondary xylem. The axial and ray parenchyma of the xylem develops protrusion and these protrusions enter or invade into the lumen of tracheids or vessels through pits. This invasion of parenchyma occurs when tracheids or vessels become inactive or damaged.
Who discovered Tyloses?
Malpighi (1686) for the first time reported the ‘balloon-shaped sacs’ in the lumen of vessels of heartwood and he named it as tyloses based on the Greek word ‘Thyllen’ meaning ‘bag’ or ‘container’.
Xylem (Structure, Composition & Classification of Primary and Secondary Xylem)
What is vascular tissue?
The tissue associated with conduction of water, minerals and food materials in plants are called vascular tissue. Plants with a well-developed conductive system are thus called as ‘vascular plants’. Vascular plants are also known as ‘Tracheophyta’ (‘trachaea’ = vessels, a component of xylem, ‘phyta’= plants).
The vascular systems in plants composed of two types of tissues
(1). Xylem: Tissue for the conduction of water and minerals.
(2). Phloem: Tissue for the conduction of food materials.
Both the xylem and phloem are complex tissues composed of more than one types of cells. Xylem and phloem are closely organized in plants. The vascular bundles found in the primary structures of plants are formed by the association of xylem and phloem.
What is xylem?
The xylem is one of the conductive tissues in plants. It is a complex tissue composed of many types of cells. The term xylem was proposed by Nageli (1858) and he derived the word from a Greek word ‘xylos’ meaning wood. The main function of xylem is to conduct water and minerals from roots to leaves. The secondary xylem also provides mechanical support due to the presence of thick lignified cell wall.
What are the components or elements of xylem?
The xylem composed of four types of cells. Among these cells, some cells are living and some are dead.
The four elements of xylem are:
(3). Xylem Fibres
(4). Xylem Parenchyma
Tracheids are the fundamental cell type in the xylem. They are elongated tube like cells with tapering ends and chisel like in appearance. The cells are non-living at their maturity and the mature cells are empty without protoplast. They have highly lignified secondary cell wall and the cells angular and polygonal in cross section. The average length of tracheid is 5 – 6 mm. Major portions of the cell wall of tracheids are perforated with pits. They also possess pit pairs between two adjacent tracheids at their common walls. Pits may be simple circular pits or advanced bordered pits.
CSIR JRF NET Life Sciences December 2016 Solved Question Paper PDF
Official / Original Previous Year (Old) Solved Question Paper of CSIR Junior Research Fellowship (JRF) and National Eligibility Test (NET) Life Sciences (XL) Examination Dec 2016 with Answer Key and Explanations as PDF. CSIR aspirants can download the question paper as single PDF file for your exam preparation. To download the question paper as single PDF file, please click on the download button below. Feel free to ask any doubts or clarifications.
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Protophloem vs Metaphloem Similarities and Difference between Protophloem and Metaphloem
Vascular bundles (fascicles) are the component of the stelar system in higher plants and their main function is the conduction of water, minerals and food materials. Typically, a vascular bundle composed of xylem and phloem arranged together as bundles. In a young stem, both in dicots and monocots, Phloem, the food conducting tissue of vascular bundles, are differentiated into PROTOPHLOEM and METAPHLOEM based on the structural and functional modifications of their elements. The present post describes the similarities and difference between Protophloem and Metaphloem in a primary vascular bundle of a young stem.
Similarities between Protophloem and Metaphloem
Ø Both protophloem and metaphloem can conduct food materials.
Ø Both are complex tissues, composed of many types of cells.
Ø Both components contain living and dead cells.
Ø Both are developed from the primary meristem, the pro-cambium.
Ø Protophloem and metaphloem develop only in primary vascular bundles.