Gymnosperms are also called soft wood spermatophytes because they lack xylem fibers.

Gymnosperms are a group of seed-bearing plants that have naked seeds, meaning they are not enclosed in a fruit. They are commonly referred to as softwood spermatophytes because they have softer wood compared to angiosperms, which are commonly referred to as hardwood spermatophytes. The term "softwood" refers to the texture and properties of the wood, which is less dense and typically easier to cut compared to hardwood.

Explanation:
To understand why gymnosperms lack xylem fibers, it is important to understand the basic structure and function of xylem tissue in plants.

Structure of Xylem:
Xylem is a complex tissue that transports water, minerals, and other substances throughout the plant. It is composed of various types of cells, including tracheids, vessels, fibers, and parenchyma cells.

Function of Xylem Fibers:
Xylem fibers are long, thick-walled cells that provide mechanical support and strength to the plant. They are responsible for the rigidity and stiffness of the wood. Xylem fibers have secondary cell walls, which are strengthened by lignin, a complex polymer that adds strength and durability.

Gymnosperm Wood:
In gymnosperms, the wood is composed mainly of tracheids, which are elongated cells with tapering ends and thick secondary cell walls. Tracheids serve both as water-conducting cells and structural support. However, gymnosperms lack xylem fibers, which are present in angiosperms.

Reason for Lack of Xylem Fibers in Gymnosperms:
The absence of xylem fibers in gymnosperms is believed to be an ancestral trait. Gymnosperms diverged from other seed plants early in evolutionary history, and they have retained some primitive features. Xylem fibers likely evolved later in the angiosperm lineage.

Implications of Lack of Xylem Fibers:
The absence of xylem fibers in gymnosperms affects the mechanical properties of their wood. Gymnosperm wood tends to be softer and less dense compared to angiosperm wood, which has a higher content of xylem fibers. This difference in wood properties has practical implications, as it affects the suitability of wood for various applications, such as construction, furniture-making, and paper production.

In summary, gymnosperms are called softwood spermatophytes because they lack xylem fibers, which are responsible for the rigidity and stiffness of wood. The absence of xylem fibers in gymnosperms is an ancestral trait, resulting in softer wood compared to angiosperms.