University:
Kentucky State University
Course:
BIO 212 | General Botany
Academic year:

2024
Views:

195

Pages:

3
Author:

pravitate8aj12

Lab.No.6 Xylem (2) Vascular Cambium & Periderm Prepared slides 1-Same slides of last lab. (Xylem) including Tilia stem c.s 2- Pinus stem c.s 3- Liriodendron stem c.s 4- Aristolochia Stem c.s Fresh specimen Celery plant. Models - Wood (hard wood and soft wood) - Tilia 1 Lab.No.6 Xylem (2) Vascular Cambium & Periderm ***1) You can restudy Xylem slides of the last lab. *** Celery plant was put in a beaker containing water, take a branch of this plant and make a cross section in the stem , make it thin as possible as you can, prepare wet mount slide using toluidine blue, examine and notice the vascular tissue, notice primary xylem 2) Vascular Cambium: -Many small, herbaceous annuals have no secondary growth at all. However, plants that grow large or persist for several years require a larger stem diameter for support, increased amounts of vascular tissue to supply greater numbers of branches and leaves. Dicots and gymnosperms undergo secondary growth by having vascular cambium, which originates from promeristems. (secondary meristem). The function of vascular cambium is to produce secondary xylem and secondary phloem There are two types of vascular cambium cells: -fusiform initial Which are elongated cells with tapering ends, produce cells of axial system - ray initials which are isodiametric and occur in groups ,it produce cells of ray system The two types of vascular cambium cells can be distinguished in tangential longtudinal section. Periderm: -The outer protective tissues that replaces epidermis in woody stems and roots. - it develops from the phellogen or cork cambium [uniserriate, thin walled cells, rectangular ,flattened cells] as a result of continuous cell division, in each division cork cambium or phellogen produces two cells one to the external side (phellem) or cork [dead cells impregnated with suberin, compact with no intercellular spaces, prismatic- irregular cells] and the other to the internal side (phelloderm) [thin walled parenchyma] - Periderm has structures that permit entry of air to the tissues of periderm called lenticels. It appears from outside as vertical or horizontal elongated mass of loose cells (with intercellular spaces between them) that protrude above the surface through a fissure. 2 Remember that both vascular cambium and cork cambium (phellogen) form the lateral meristems ***1) Examine a prepared slide for Liriodendron stem c.s Notice the following -Secondary xylem, secondary phloem -cells of vascular cambium between secondary xylem and secondary phloem, notice the shape of these cells and if there is any difference between them (flattened cells) -periderm, try to differentiate between different cells of periderm (phellem, phellogen and phelloderm) notice if there are lenticels, examine their structure. ***2) Examine prepared slide for Pinus stem c.s (conifers) Notice the following: -Secondary xylem (uniform in contents) - secondary phloem -examine in detail the shape of vascular cambium located between secondary xylem and secondary phloem. - resin ducts in xylem tissue - tanniniferous cells in pith and phloem ***3) Examine a prepared slide of Aristolochia stem Examine the layers of periderm and the structure of lenticels. 3

Xylem (2) Vascular Cambium & Periderm

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