Question

5. The following questions are based on the drawings of root or stem cross sections shown in the figures. (15 points) (1). Refer to the figure. An eudicot root is represented by (2). Refer to the figure. A woody eudicot is represented by (3). Refer to the figure. A monocot stem is represented by (4). Refer to the figure. An eudicot stem is represented by (5). What type of plant growth does Figure I, II, or III represent? What type of plant growth does Figure IV represent? Describe these two types of plant growth.

Answer 1

1) Eudicot root is represented by I (first figure): Eudicot = Eu means True, i.e. True dicots, they are also known as tricopates it includes most of the plants conventionally described as dicots. These have xylem in the form of 'X' as shown in figure I ,surronded by phloem also contains tap root and the amount of xylem and phloem is continuous. In a transverse section, vessels of xylem are in angular and polygonal shape.

2) A woody Eudicot is represented by IV (fourth figure): Simlarly, as stated above Eu = true, therefore they are also known as woody dicots. These have an outer membrane known as periderm then followed by a cork cambium, also on the out ring they have secondary pholem somewhat conical in shape with point side towards the edge arrange concentrically as shown the figure IV, while on the inner ring they have Secondary xylem which has summer wood and spring wood. In between the Secondary xylem and phloem lies the Vascular cambium.

3) A Monocot stem is reprented by II (second figure):Unlike Dicots, monocot stems does not have secondary xylem and phloems. Structure of xylem is somewhat circular and are arranged in the shape of V. Vascular Bundles are in large number and scattered in the ground tissue as shown the figure II.Cambium is absent in monocot stem.

4) A Eudicot stem is represented by III (third figure): Also known as a true dicot stem, posses single layered epidermis with a thick cuticle, vascular bundles are in similar sizes, mostly wedge shaped, arranged in one to two rings concentrically as shown the figure III.Secondary growth is presnet due to formation of lateral meristem.

5) Plant growth in I,II,III represents Primary Growth: It adds to the length of the plant due to divisions in the apical meristem,protoderm,procambium, and ground meristem.It leads to the development of lateral appendages, a way in which new cells are added in the plants. Basically the influence of the apical meristem/bud is to dominate the rest(axillary bud growth) of the plant growth besides its length also known as apical dominance.

Plant growth in IV represent Secondary Growth: It is referred to as the formation of Secondary tissues with help of lateral meristems, basically it thickens the width of the plant i.e increases the diameter and adds to the bulkyness of the plants, hence provides protective covering to the plants. It is mostly observed in Woody plants, also occurs in some dicots but very rare in monocots.