Phloem

Introduction to phloem

1. Name Muhammad Adnan Roll No BBOF18BM010 Submitted To Ma’am Rabia Saba Subject Plant Anatomy Topic Phloem BS-BOT( 6 th ) University of Sargodha Sub campus Bhakker

2. Content Phloem Classification of phloem Competents of phloem Sieve Elements 1) Sieve cells 2) Sieve tubes Companion Cells

3. Phloem It is type of complex tissue found in the vascular system which may also becalled bast or leptome. Usually phloem is present external to xylem In leaves phloem is located on the abaxial side (lower side)

4. Internal phloem: phloem present internal to xylem External phloem: phloem present external to xylem Intra-xylary phloem: new term describing internal phloem Inter-xylary phloem: phloem seen included inside the secondary xylem (iti s also called as included phloem)

5. Classification of phloem Based on development, two types of phloem 1. Primary phloem 2. Secondary phloem Primary phloem derived from pro-cambium during primary growth Secondry phloem formed from vascular cambium during secondary growth

6. Components of phloem Phloem composed of several elements Thecomponents of phloem are: 1. Sieve elements 2. Companion cells 3. Phloem parenchyma 4. Phloem fibres and Sclereids

7. 1. Sieve elements Living cells inthe phloem With protoplasm No lignified secondary cell wall Sieve elements are of two types: I. Sieve cells Il. Sieve tubes

8. Sieve cells These are narrow elongated cells without conspicuous sieve areas, and taper at their ends or have greatly inclined walls which overlap in the tissue. These are found among members of lower vascular plants and gymnosperms

9. Sieve tubes Advanced type of sieve element Occurs in angiosperms Longitudinal series of cells Each cell is called sieve tube member or sieve tube element Sieve area are located on the end wall Sieve area are more specialized in sieve tubes than sieve cells Sieve plate: the part of cell wall bearing sieve area End wall of sieve tube inclined to transverse The sieve plate is the more specialised area found usually in or near end wall.

10. Companion cells These are specialised parenchymatous cells found Slane Associated with sieve elements in origin, position and function. Pues Mevelof from same. meristematic cell that gives rise to the sieve element. Such a meristematic cell divides longitudinally and one of them differentiates into sieve tube and other into companion cell,

11. Normally, a single companion cell is founc aor a eve tube in thé primary phloem, but in certain plants, such as carrot, more than one cell have been reported. However, solitary long companion cells are common in primary phloem, and in groups, in secondary phloem. In a cross-section, the companion cell appears rounded OF polygonal, These are living cells and have dense cytoplasm, prominent nucleus, several " vacuoles, and other cytoplasmic organelles. Starch grains are never found in. ‘€ompanion cells.

12. Thank you