What is the Difference Between Protoxylem and Metaxylem?

Protoxylem and metaxylem are two components of primary xylem, which is responsible for the transportation of water and minerals in plants. The main differences between protoxylem and metaxylem are:

1. Formation: Protoxylem is the first formed primary xylem, maturing before the plant organs complete their elongation, while metaxylem is the later formed primary xylem, maturing after the completion of plant organ growth.
2. Cell Size: Protoxylem has smaller cells, making it less prominent, whereas metaxylem has larger cells, making it more prominent.
3. Lignification: Protoxylem has limited lignification, making it less effective in conducting water, while metaxylem has extensive lignification, making it more effective in conducting water.
4. Water Conduction Efficiency: Metaxylem is more efficient in water conduction compared to protoxylem.
5. Location: In a stem, protoxylem is located towards the outside, while metaxylem is located towards the inside.
6. Cell Wall Thickenings: Protoxylem has annular or spiral thickenings around the vessels, while metaxylem has reticulate, scalariform, or pitted thickenings around the vessels.

In summary, protoxylem is the first primary xylem formed during plant growth and has smaller, less effective cells for water conduction, while metaxylem is the later formed primary xylem with larger, more effective cells for water conduction.

Comparative Table: Protoxylem vs Metaxylem

Here is a table summarizing the differences between protoxylem and metaxylem:

Both protoxylem and metaxylem are primary xylem elements responsible for water and mineral conduction, and they contain living and dead cells. They develop from the primary meristem, pro-cambium, and contain tracheids, vessels, and parenchyma.