*3.1.1 Vascular bundles*

Vascular bundles serve as the supporting structure and the transport system of the oil palm fronds. Typically, the vascular bundles are composed of fibre, vessel or metaxylem, protoxylem, protophloem or sieve tubes, axial parenchyma, stigmata, and companion cells [30, 32]. Most of the vascular bundles are composed of one or two-vessel cells. Though uncommon, vascular bundles with more numerous than three vessels designed tangentially or in batches can also be observed scattered, especially in the core section. Widespread protoxylem lessened vascular tissue, and little bundles with tiny fibrous tissues are also regularly seen scattered between the broader bundles in the core section. The arrangement of fibrous strands depends on the amount of bundles present [33]. Phloem can be found located between the vessel and fibre sheath. Protoxylems are present at the outer part adjacent to the vessel. The number of vascular bundles for the frond is the same and permanent. The growth is happening on vascular bundles diameter only and not its quantity [34].

Based on the visual investigation under SEM, the vascular bundle consists of one or two large vessels and surrounded by fibres cells (**Figure 7**). These vascular bundles are embedded around parenchymatous tissue. The vascular bundles are surrounded by parenchymatous ground tissue. Therefore the wood material from this species is not comparable to the woods produced from both dicotyledons and gymnosperms species which developed from the secondary xylem [35]. The fibres that compose the vascular bundles are arranged in a crescent-shaped sheath surrounding the phloem. The fibres are irregular in length and wall thickness. The number of fibres associated with vascular bundles and the number of secondary walls deposited in them on the location of the bundles within fronds [36].

*Processing and Properties of Oil Palm Fronds Composite Boards from* Elaeis guineensis *DOI: http://dx.doi.org/10.5772/intechopen.98222*

**Figure 7.** *SEM of vascular bundle in oil palm fronds at the transverse sectional view (100 magnification).*
