Chapter 31, pages 668-691
Plant Anatomy-1 9:59-19:05
Plant Anatomy-3 19:43-30:30
I. Primary Tissues of the Procambium
A. Primary Xylem
1. Differentiates four kinds of cells
a. Tracheids
b. Vessels
c. Fibers
d. Parenchyma
2. Tracheids
a. One of two types of conducting cells in the xylem
b. Dead when fully mature and functioning
c. Contains lignin
d. Morphology of the tracheid cell
(1) Very long and thin cell
(2) Ends of cell with long oblique cross wall
e. Contain pits
(1) Structure of the cell wall
iii. Secondary Cell Wall
(2) Structure of a simple pit
i. Pits are depressions in
the cell wall that are circular to oval where the
secondary cell wall
is the portion of the cell wall that is hollowed out
to make the pit
ii. Pits are adjacent to one another on either side of the cell wall
iii. Thus, pits come in pairs and are called pit pairs
iv. The pit membrane is composed of the primary wall and middle lamella of the adjacent cell walls of the pit pairs
v. U-shaped in morphology
vi. Found in parenchyma, collenchyma, fibers, and sclerids
(2) Structure of the Bordered Pit
i. Similar to the simple pit
ii. The
secondary
cell wall forms a border over the
pit
membrane leaving a
small opening called
a
pore
iii. In the center of the pit membrane
is a knob of secondary tissue called a
torus
iv. The torus can swell to the
extent of plugging the pore in the border and
prevent water
loss during water stress in the plant
v. In tracheids, vessels, and xylem fibers
a. One of the two conducting cells of the xylem, the other one is the tracheid
b. Dead when mature and functioning, contains lignin
c. Morphology of the vessel element
(1) Thick cell walls
(2) Cross walls
i. Many times are missing in the mature cell
ii. At most will contain large
holes or just bars of tissue to keep the end of
the cell from collapsing
iii. Will be almost horizontal in
some to slanted in others but not as slanted
as in tracheids
(3) Cells are much shorter than tracheids
(4) Cells are much wider than tracheids
(5) Contain characteristic
secondary
wall thickenings (annular, reticulate, pitted,
scleriform, etc.)
4. Fibers
5. Parenchyma
a. Used for lateral transport
b. Used for food storage
1. Thin layer of
procambium
that remains undifferentiated between the xylem and
phloem
2. Remains meristematic
3. Destined to become the vascular cambium
II. Pith and Pith Rays
A. Pith - large parenchyma cells in the center of the vascular bundle ring
1. Used for food storage
2. Used for waste storage
B. Pith rays - large parenchyma cells between the vascular bundles
1. Used for food storage
2. Used for lateral transport of food and water
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