Page 25 - Demo 1

In contrast to parenchyma and collenchyma cells, sclerenchyma cells
have thick secondary cell walls containing lignin, which provides cells with
strength and rigidity. Most sclerenchyma cells are nonliving and do not contain
living cytoplasm. Their primary funcon is to support the mature regions of the
plant. There are two types of sclerenchyma: fibers, which are long, slender
cells that usually form strands and sclereids, which are variable in shape but
oen branched. Clusters of sclereids are responsible for the griy texture in the
flesh of pears. The long fibers in plants, such as coon and flax, can be woven
into cloth; and hemp fibers can make a strong rope.

Figure 9. Sclerenchyma cells with thick and tough secondary walls
Source:
https://upload.wikimedia.org/wikipedia/commons/thumb/0/07/Plant_cell_type_sclerenchyma_fibers.png/220px-Pl
ant_cell_type_sclerenchyma_fibers.png

Vascular Tissue

Vascular ssue extends from the root through the stem to the leaves and
vice versa. In the root, the vascular ssue is found in a central cylinder; in the
stem, vascular ssue occurs as mulple vascular bundles; and in the leaves, it is
located in the leaf veins. Vascular ssue is composed of xylem and phloem,
which funcon in the transport of water and dissolved substances.

The xylem is the plant’s primary water-conducng ssue, forming a connuous
system that runs throughout the plant body. Xylem contains two types of
conducng cells: vessel elements and tracheids. Both types of cells are hollow,
but the vessel elements are larger, have perforated end walls, and are lined
up from end to end to conduct water and minerals. The end walls and side
walls of tracheids have pits that allow water to move from one tracheid to
another. Vessels conduct water more efficiently than strands of tracheids.

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