Question

Exercise II Histology of the Leaf PART A. MESOMORPHİC LEAF: SYRINGA VULGARIS Examine a prepared slide containing a transverse section of a Syringa (lilac) or another mesomorphic leaf. At first, use the microscope's 10x objective, then switch to the 43x objective. With the 10x objective in place, note the variation in size and orientation of the veins (vascular bundles), which contain the two vascular (conducting) tissues, xylem and phloem. The centrally located largest vein is the midvein. The midvein and its associated ground tissue constitute the midrib of the leaf (see text Figure 25-2la, page 594). 1. What is the function of the reinforced midrib? All veins in the Syringa leaf are collateral bundles, with the xylem occurring above the phloem. 2. How does this position of xylem and phloem relate to that of a vascular bundle in the stem? The midvein in Syringa contains a vascular cambium and undergoes a limited amount of secondary growth, secondary xylem being produced toward the upper surface of the leaf and secondary phloem toward the lower surface. The smaller veins contain only primary xylem and primary phloem and are surrounded by a bundle sheath. Examine a portion of the lamina (see text Figure 25-21b, page 594) that is to one side of the midrib and identify the upper epidermis, which has a relatively thin but discernible cuticle; the palisade parenchyma; the veins, with bundle sheaths and those with bundle-sheath extensions; the spongy parenchyma; and the lower epidermis, which also has a cuticle. The

Answer 1

1. The mid rib is centrally located in a leaf and it provides support for the leaf and carries cell sap upto the leaf .it helps the leaf the leaf to keep in an upright position and to keep the strong and protect it from wind and other forces . It's the primary vein which consists of xylem and Pholeum to conduct water from stem up to the lead blade and transport food from leaf to other parts of plant

2

The xylem tissue occured in between pholeum tissue In spryinga plant .Pholeum occured in a ring like structure around the xylem in stem as there is more pressure gradient of water in xylem tissue Ptolemy usually takes radial position in stem as compared to leaves.