Question

Cut a transverse section of young stem of a plant from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem? Give reasons.

Answer 1

Procedure and observation:

A thin transverse section (T.S.) of the young stem is cut, stained and observed under the microscope. Based on the anatomical characters seen in the section, the stem can be identified as monocot or dicot.

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Identification as Dicot stem:

The stem is identified as a dicot stem if the following features are observed:

• Vascular bundles are arranged in a ring near the periphery. 
• Each vascular bundle is open (presence of cambium between xylem and phloem). 
• A distinct cortex, endodermis, pericycle and central pith are present. 
• Medullary rays are present between vascular bundles.

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Identification as Monocot stem:

The stem is identified as a monocot stem if the following features are observed:

• Vascular bundles are scattered throughout the ground tissue. 
• Vascular bundles are closed (cambium absent). 
• Cortex, endodermis and pith are not clearly differentiated. 
• Each vascular bundle is surrounded by a sclerenchymatous bundle sheath.

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Conclusion:

Thus, by observing the arrangement and nature of vascular bundles, presence or absence of cambium, and differentiation of ground tissue, it can be ascertained whether the given stem is monocot or dicot.