Functional Plant Biology

Questions: 1. Compare the woody dicot tissues with the pine (polycot) tissues. 2.How does the polycot roots differ from the woody dicot roots? 3.Examine the prepared slide of the pine root. How does it compare to the pine stem? Answers: 1. The pine trees are classified in the gymnosperms class. These are plants having naked seeds. This species have different cotyledons in their seeds and thus referred to the polycots. In the dicot plants, the vascular bundles within the stem are arranged in a cylindrical form. In woody dicots, a cut across the stem would appear as a ring spot. The leaf veins in the woody dicots are usually net like. In woody dicot tissue, the secondary growth occurs due to the lateral meristem activity including vascular cambium and cork cambium. In secondary growth, the root and stem tissues grow and enhance the girth of the plant (Hodson and Bryant 2012). The stem or root of the plants continues to grow as long as the lateral meristem produces new cells. In woody dicots, this procedure led to the formation of wood and thickened the tree trunk, thereby turning the plant into the tree. The secondary growth ruptures epidermis tissue of root and stem, develops cork cambium and gives rise of cork cells for protecting plant surface. In contrast, the pine (polycot) trees contain several cotyledons (Hodson and Bryant 2012). They lack vessels in the xylem tissue. Pine trees have only the tracheids and resin ducts in their leaves, thereby providing needle-shaped leaves. In contrast, the woody dicots have both tracheids and vessels. 2. In woody dicot root, the xylem tissue is like 3 or 4-prolonged star. The root contains xylem and phlooem tissues. While comparing the root system of polycots and woody dicots, both the woody dicots and polycot always produce secondary root system in their taproot and main branch root. The root system of polycot and woody dicot consist of coarse roots that are more than 2-3 cm in diameter. In dicot roots, the xylem and phloem tissues are surrounded by endodermis, known as the stele (Hodson and Bryant 2012). The pine roots have three anatomically distinct zones. The terminal region is the condensed tannin zone and the white roots are efficient for ion uptake. The tannin zone include dead cortex. The young cork zone is dedicated to the little amount of ion and water uptake. In dicot plants, the pericycle gives rise of the lateral roots, cork cambium and vascular cambium and promotes secondary growth. The pith is absent in the woody plants. All of these tissue features promote cork ti ssue development in the woody dicot (Luuttge 2012). 3. The cross-section of pine stem shows different concentric rings with distinct borders within each ring. The center of the stem is known as pith containing many large cells. An annual cycle ring is also shown on the stem. Several large holes were seen which are like water pipes. Cortex is found around the edge of the stem those are bubble-like objects and circular in shape (Luttge 2012). Dissection of a pine root revealed bands of cells that are known as the rays and scattered resin ducts. These rays are composed of thin-walled live parenchymal cells disintegrated after the wood dries. The root has several tiny holes which are speculated to be the water pipes of the root. Xylem is the middle layer consisting gigantic holes and the edge of the holes are red. In context, the resin ducts are found as dark dust sticking to the layer (Hodson and Bryant 2012). Reference List Hodson, M. and Bryant, J., 2012. Functional plant biology. Chichester, West Sussex, UK: John Wiley Sons. Luttge, U., 2012. Progress in botany. Berlin: Springer.