Question

When protoxylem is surrounded by metaxylem, it is
(a) Mesarch condition
(b) Endarch condition
(c) Exarch condition
(d) None of the above

Answer 1

Hint: Protoxylem is the first formed xylem and metaxylem is formed after protoxylem. Both are made up of tracheids and vessels. Exarch condition gives rise to protoxylem outside metaxylem, endarch condition leads to protoxylem inner to metaxylem and in mesarch condition protoxylem form inner side of metaxylem.

Complete answer:
Based on the position of protoxylem and metaxylem, xylem is grouped into exarch, endarch and mesarch. In exarch condition protoxylem lies outside if metaxylem in linear form and endarch condition the protoxylem lies inside of metaxylem in linear form whereas in mesarch condition metaxylem are present in circular form and inside the metaxylem protoxylem are present in middle.

Additional Information:
Xylem is a complex tissue that helps in the absorption and conduction of water and minerals and it also strengthens plants and their part by mechanical support. Xylem forms a continuous channel from root to stem to leaves and then to fruits and flowers. Xylem shows three types of components like tracheid element, xylem parenchyma which is also known as wood parenchyma and xylem or wood fibres. The tracheids and fibres are made up of dead cells therefore they mainly function for mechanical support whereas xylem parenchyma is made up of living cells and functions for storage of food and conduction of water and sap.

So, the correct answer is 'Mesarch condition'.

Note:
Out of all xylem components only tracheary elements like tracheids and vessels help in the transportation of sap, in which vessels are the main tracheary element in angiosperm. The conducting element was called Hadrome by the German botanist Haberlandt.