The Leaf

Lab 10 (The Leaf) Prepared Slides: 1- Syringa leaf c.s 2- Zea mays leaf c.s 3- Pinus leaf c.s 4- Ginkgo leaf c.s 5- Cycas leaf c.s Fresh Specimens 1- different monocot and dicot leaves 2- woody twig Lab 10 The leaf -Leaves are the primary photosynthetic structures in most plants. -Leaves vary in form and internal structure depending on habitat and type of photosynthesis carried out by plants. 1) Types of leaves A) Dicot leaves Exercise 1 Examine a prepared slide of Syringa leaf c.s Notice the following: -bifacial leaf structure (palisade parenchyma on the upper side and spongy parenchyma on the lower side of the leaf blade.) -uniseriate upper epidemis -palisade mesophyll loctaed on the upper (adaxial: directed towrds the axis ) side on the blade and is made of compact elongated chlorenchyma -spongy mesophyll layer on the lower (abaxil: directed away from the axis) surface of the blade and is made up of loose chlorenchyma with abundance of intercellular spaces -Uniseriate lower epidermis -amphistomatic leaf (stomata occurring on both the upper and lower epidermis) , substomatal air spaces, are spaces adjacent to stomata -collateral vascular bundle, are embedded in the mesophyll and are enclosed in the bundle sheath which are connected with the epidermis by bundle sheath extension are made up of sclerenchyma ), large vascular bundles are enclosed by parenchyma which make the vein rib that arise above the epidermal level, collenchyma may occur in vein ribs ( one of them is the mid vein ) -ends of the veins are seen in longitudinal form in the mesophyll B) Moncot leaves Exercise 2 Study a prepared slide of Zea mays leaf c.s Notice the following: -uniserite upper epidermis with enlarged bubble like epidermal cells called bulliform cells -no differentiation in the mesophyll into palisade and spongy layers (unifacial leaf) -uniserite lower epidermis -amphistomatic leaf -collateral vascular bundles the are uniform in size and arrangement, small vascular bundles are enclosed in a single-layered parenchyma epidermis by sclerenchyma cells C) Gymnosperm leaves In general, variation in gymnosperm leaves is not as great as it is angiosperm leaves Exercise 3 Study a prepared slide of Pinus leaf c.s Notice the following -thickh-walled epidermis and cuticle -sunken stomata with prominent subsidiary cells and substomatal cavity -subepidermal sclerenchymatous hypodermis -plicate mesophyll of floded parenchyma with resin canals -well-differentiated endodermis -vascular system is enclosed in transfusion tissue which is made up of tracheids and parenchyma cells. Group of albuminous cells is recognized in the phloem region Exercise 4 Study a prepared slide of Ginkgo leaf c.s Notice the following -bifacial leaf -uniseriate thin-walled epidermis -hypostomatic leaf (stomata present in the lower epidermis only) stomata is slightly sunken -palisade mesophyll is made up of a single layer of short lobed cells -spongy mesophyll is made up of aerenchyma -numerous vascular bundles each is surrounded by lignified endodermis -some transfusion tissue occurs along the sides of the vascular bundles -mucilage ducts are located in the mesophyll alternating with the vascular bundles Exercise 5 Study a prepared slide of Cycas leaf c.s Notice the following -bifacial leaf -uniseriate thick-walled epidermis with thick cuticle -subepidermal sclerenchymatous hypodermis -hypostomatic leaf -sunken stomata with substomatal cavities -palisade mesophyll is made up of elongated cells, the median layer of cells elongated perpendicularly to the single vein (accessory transfusion tissue), the lower layer is made up of short cells -spongy mesophyll with small intercellular air spaces -single vascular bundle enclosed in sclerenchymatous sheath -transfusion tissue occurs on both sides of the xylem Exercise 6 Examine fresh specimens of different types of leaves and notice the following -shape of leaf blade (lamina), differentiate between the adaxial and abixal sides -presence or absence of petiole (petiolated or sessile) -presence or absence of sheath and ligules at the base of leaf blade of monocot leaf - the arrangement of veins (venation) [parallel, netted (reticulate, palmate, pinnate or longitudinal)] Exercise 7 Examine the leaf blades of a monocot and a dioct leaves using the dissecting microscope, notice the venation and the epidermis. Make a paradermal section in these leaves and examine using the compound microscope, try to find differences between these leaves in paradermal section. Leaf abscission Exercise 8 Make a longitudinal section through the nodal region of a woody twig including a portion of the mature leaf petiole of the stem try to identify layers of abscission zone (separation layer(densely stained along which break occurs) and the protective layer with suberized cells )