Leaf Anatomy: A Comprehensive Guide PDF

# Leaf Anatomy By: Dr. Abeer Sayed Moawad ## Cytology and Plant Cells - Cytology is the scientific study of cells; the unit of the living organisms - A plant cell is characterized by the presence of cell wall surrounding plasma membrane which encloses where cellular organelles are found; the cyt...

# Leaf Anatomy By: Dr. Abeer Sayed Moawad ## Cytology and Plant Cells - Cytology is the scientific study of cells; the unit of the living organisms - A plant cell is characterized by the presence of cell wall surrounding plasma membrane which encloses where cellular organelles are found; the cytoplasm together with the nucleus is called the protoplasm. The nucleus carries the hereditary material. ## Features of Plant Cells The main features that characterize plant cells from other eukaryotic organisms are: - **Presence of cell wall** composed of cellulose, hemicellulose, pectin, lignin (c.f cell wall of fungi made of chitin and cell wall of bacteria made of peptidolignan). - **Presence of plastids** - **Presence of large vacuole** - **Presence of plasmodesma** that connect the protoplasm of neighboring cells ## Plant Anatomy Also known as Micromorphology of plants and plant histology, is concerned with the microscopic structure of the cells, tissues, and organs of plants. ## Tissues - **Group of cells with identical form and function is known as tissue** ### Plant Tissue Types Plant tissues are divided into three main groups. - **Dermal tissues** - **Ground tissues** - **Vascular tissues** ### Dermal Tissues - Occurs on the surface of plants and it is a complex tissue consisting of epidermal cells, stomata and trichomes (hairs). #### Epidermal Cells 1. Single layer 2. No intercellular spaces 3. Show different shape, size, and arrangement (from plant to another). Cell wall may be straight or wavy walls. 4. Covered with a cuticle (water impermeable substance; cutin), may be smooth, warty, or striated 5. Upper epidermis differs from the lower epidermis #### Stomata - These are openings in the epidermis. - A stomata is made of pair of similar cells, called guard cells, having a pore in the center called osteole for gaseous exchange. - They occur in both surfaces or only on lower surface. - The epidermal cells surrounding the stoma are called subsidiary cells. - Based on the arrangement of the subsidiary cells, stomata are divided into four different types. ##### Types of Stomata 1. **Ranunculaceous** or **Anomocytic:** The surrounding cells (subsidiary cells) are of similar size. Example: Digitalis. 2. **Cruciferous** or **Anisocytic (unequal celled):** The stoma is surrounded by usually three unequal-sized subsidiary cells. Example: Belladonna. 3. **Paracytic** or **Rubiaceous (parallel celled):** The stoma is surrounded by two subsidiary cells and have their long axes parallel to the osteole. Example: Senna. 4. **Diacytic** or **Caryophyllaceous (cross celled):** The stoma is surrounded by subsidiary cells having their long axes perpendicular to the osteole. Example: Mentha. #### Trichomes (Hairs) - Hairs are outgrowths (projections) of epidermal cells of variable shape and size. - If it is short and conical, it is called papillae and the epidermis is described as papillosed (e.g. Coca). If the projections are long, they form trichomes or hairs. - Hairs are classified into glandular and non-glandular. ##### Non-Glandular Hairs - These are formed of one cell or more. - They can be unbranched or branched ###### Unicellular Non-Glandular Hairs 1. **Cottony** 2. **Cystolith** 3. **Papillae** ###### Multicellular Non-Glandular Hairs - **Unbranched:** 1. **Uniseriate** 2. **Biseriate** 3. **Pluriseriate** - **Branched:** 1. **Simple** 2. **Peltate** 3. **Candelabra** 4. **Stellate** ##### Glandular Hairs - These are very similar in their shapes to the non-glandular types, but they have glands on their heads which differentiate them from the non-glandular types. This is a very important feature in the plants' identification process. ###### Types of Glandular Hair Stalk Structure - **Unicellular Stalk:** - **Unicellular Head:** Example: Mentha. - **Bicellular Head:** Example: Digitalis. - **Multicellular Head:** Example: Labiaceous hair in Mentha and clavate hair in Belladonna. - **Multicellular Stalk:** - **Uniseriate Stalk** - **Biseriate Stalk** and **biseriate head** or **compositae type** - **Pluriseriate Stalk** and a **head with multicellular head** - **Branched Stalk:** The branch ending in head. ## Describe the following trichomes: - **1.** Stellate non-glandular hair - **2.** Simple branched, non-glandular hair - **3.** Bicellular head with unicellular stalk glandular hair - **4.** Peltate non-glandular hair - **5.** Uniseriate, unbranched, non-glandular hair - **6.** Multicellular head with multicellular stalk glandular hair - **7.** Candelabra non-glandular hair - **8.** Branched, non-glandular hair - **9.** Uniseriate, unbranched, non-glandular hair