Question

Mesarch xylem is a characteristic of
A. Stems of seed plants
B. Stems of aquatic plants
C. Roots of seed plants
D. Leaves of seed plants and pteridophytes

Answer 1

Hint: In the mesarch type of arrangement of xylem, the protoxylem develops first in the primary xylem in the center of the strand, and then it continues to develop in both, outer and inner sides of the strand. Higher plants don’t have this type of xylem arrangement.

Complete answer:
Xylem transports water and some other mineral nutrients from the roots to the leaves of the plants and is one of the two types of vascular tissues found in plants. Different types of xylem arrangements are found in different plants and also in different parts of the same plant. Mesarch type of xylem arrangement has been seen in the plants belonging to pteridophytes and such xylem is the characteristics of these plants.

Additional information:
Considering the development of xylem, protoxylem is the first xylem that develops in a growing plant and it has vessels with the narrow lumen. Based on the arrangement of protoxylem and metaxylem, the types of xylem can be –
- Centrarch – In this type of arrangement, the protoxylem is surrounded by metaxylem, but this type of arrangement is not found in any presently living plants.
- Exarch – Here, protoxylem is towards the outer side while metaxylem is towards the inner side and the arrangement is found in the roots of vascular plants.
- Endarch – This arrangement is opposite to the exarch here, protoxylem lies towards the inner side and metaxylem towards the outer side and such type of arrangement of xylem elements is shown by the stems of vascular plants.
- Mesarch – Here, protoxylem in a primary xylem strand develops first in the center of one strand and it continues to develop both centrifugally and centripetally. This type of arrangement is found in the leaves and stems of ferns and pteridophytes.

So, the correct answer is “Leaves of seed plants and pteridophytes”.

Note: Tracheids and vessels are the main types of cells that constitute xylem in plants. Tracheids are long cells that besides providing sap transport, also help in structural support.
Vessels are shorter than tracheids in length but are also conducting in nature and help to conduct water mainly. These are absent in gymnosperms but are found in other flowering plants.