6. Using your textbook and looking at the prepared slides of the Ranunculus root

Question

6. Using your textbook and looking at the prepared slides of the Ranunculus root and Tilia stem (both eudicots) in the lab instructions: a. describe the arrangement of xylem and phloem in an angiosperm eudicot root. b. describe the arrangement of xylem and phloem in an angiosperm eudicot stem. c. looking at figures in your textbook, explain how the locations of xylem and phloem in a cross section of a monocot root differ from those in a eudicot root. d. looking at figures in your textbook, explain how the locations of xylem and phloem in a cross section of a monocot stem differ from those in a eudicot stem

Explanation / Answer

6 a. There are 2-4 xylem patches found inside the endodermis of a eudicot angiospermc plant. Xylem is composed of protoxylem (primary xylem, narrow lumen, tylosis is absent) and metaxylem (secondary xylem, broad lumen, tylosis is observed). In Fig. 6 the bigger polygonal cells are metaxylem can be easily seen. However, in Fig 5, the smaller polygonal cell towards periphery, called protoxylem can be easily identified and the bigger polygonal cells towards pith, namely, metaxylem can be easily seen. There are 2-4 phloem patches found in between the xylem patches in case of eudicot angiospermic root. A cambium ring forms in between the xylem and phloem, to perform the secondary growth as a result the diametric growth takes place. As, protoxylem is present towards outside thus, the condition of the vascular bundles is known as exarch.

6 b. In case of eudicot angiospermic stem, the number of vascular bundles (xylem+phloem) are countable and they are arranged in a ring if we will observe the transverse section of the stem. Xylem and phloem occurs on the same radius, however, they are separated by vascular cambium. Thus, they are conjoint (xylem and phloem on the same radius) and open (vascular cambium is present). Protoxylem is found towards pith thus, the condition is endarch.Vascular cambium present the xylem and phloem becomes active at the time of secondary growth to form secondary xylem and secondary phloem.

6 c. If we compare monocot root with the eudicot root, there are polyarch xylem bundles i.e. their number is more than 6 in contrast to eudicot root where the number is between 2-4. Pith is well developed in monocot root in comparison to eudicot, where it is very less developed. Monocot root does not undergo secondary growth, whereas, the eudicot root does undergo secondary growth to increase the latitudinal growth of the plant.

6 d. If we compare the monocot stem with the eudicot stem figures, we can easily trace that the number of vascular bundles are more in the monocot stem and they are scattered. However, in the eudicot stem the number of vascular bundles are less and arranged in a ring. Pith is well developed in the eudicot stem in contrast to monocot stem where it is poorly developed. Vascular bundles in monocot stem are conjoint, endarch and close (cambium absent). Vascular bundles in eudicot stem are conjoint, endarch and open ( cambium present). Secondary growth is absent in monocot stem because there is no vascular cambium. However, secondary growth takes place in eudicot stem because vascular cambium is present. Thus, eudicot angiospermic plants show diametric growth.

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