Question

Describe the arrangement of vascular bundles in a cross-section of a Zea mays stem. Are they more abundant in the periphery of the stem? Explain any mechanical advantage in their arrangement.

Answer 1

Answer:

In monocots, clusters of xylem and phloem tissue, called vascular bundles, are scattered throughout the stem, as shown in the cross section below left. In most dicots and gymnosperms, vascular bundles are arranged in a cylinder, or ring, as shown in the cross section below right.

Answer 2

The vascular bundle type of Zea mays ( corn ) is of collateral i.e xylem and phloem are usually arranged opposite to each other in the vascular bundles. The phloem is usually situated outside while the xylem is at the inside. It is a kind of closed bundle without fascicular cambium.

• The phloem and xylem are surrounded by a bundle sheath of parenchyma.
• These bundle sheaths can be sclerotic and often starch-containing ones. They are rich in chloroplasts.
• The advantage of this arrangement is that the products of photosynthesis can be quickly transferred from the bundle sheath to the adjacent phloem tissue for transport to other parts of the plant.
• Vascular bundles are often scattered in corn but while observing the cross-section, it is evident that they do occur abundantly in the periphery of the stem.
• Central bundles are usually larger than peripheral ones.
• The phloem has a highly organised appearance. Sieve tubes are the ones with the greatest diameters whereas the companion cells are smaller.
• The xylem consists of large metaxyelm vessel members and smaller protoxylem.