1. Xylem is the water-conducting tissue found in tracheophytes. It is composed of tracheary elements, fibers, and parenchyma cells. 2. Tracheary elements include tracheids and vessels. Tracheids are imperforate while vessels have perforations along their length. 3. Phloem is the food-conducting tissue. It consists of sieve elements, companion cells, and parenchyma. Sieve elements transport sugars and other molecules between source and sink tissues.

1. 1/13/2010
Found in Tracheophytes
Complex Tissue
Found in some seedless plants
Cell types and development
Principal water conducting tissue 1. Tracheary elements– tracheids and vessels
Support -- elongated
Storage --lignified secondary walls
Primary xylem--procambium --dead at maturity
Secondary xylem—vascular cambium
TRACHEIDS vs. VESSELS
--which is imperforate and only have pit pairs in
their common wall?
--which has perforations?
1

2. 1/13/2010
Lacking both P and S walls
Part of the wall bearing perforation ---
PERFORATION PLATE
Where is perforation plate located?
Perforation Plate
a. simple
b. multiple
- sclariform
-reticulate
-foraminate
Multiple perforations
Common in tropical high mountain floras
Temperate and mild mesothermic climate
Pits– simple and bordered
Scalariform occur in latest formed primary xylem;
Non-seasonal mesic habitats secondary xylem
Pit pairs
Vessel- continuous tube; may contain at least or In Conifers
hundreds or thousands of vessel elements
– torus
Wider vessels– roots; lianas --margo– flexible
The basipetal increase in diameter is accompnained *aspirated condition
by decrease in density -- crassula ( thickening of ML and P wall)
2

3. 1/13/2010
Vessels vs. tracheids?
Vessel pit membrane vs. torus-margo
membrane (conifers tracheids)?
Wide vs. narrow vessels?
CAVITATION
--formation of cavities within the conduits
resulting in breakage of the water columns
--Embolism- air blockage
-- CAUSES: Freezing and Drought
Arrange the ff.
from most prone
To least prone to
freeze induced AIR SEEDING
embolism When tension exceeds the
a. Wide vessel surface tension at the air-water
b.
b Narrow meniscus spanning the p
p g pores in
vessel the pit membrane, air may be
pulled into a functional conduit
c. Tracheid
conifer
2. Supporting elements– FIBERS 3. Parenchyma
* fiber-tracheids * ray parenchyma and axial parenchyma (2 X)
* Libriform fibers -- lignified S walls
* Septate fibers (eudicots and tropical hardwood) -- simple p almost always
p pits y
– retain protoplast at maturity
* storage: starch, fats, tannins or crystals
--storage of reserve materials
* tyloses– secreted by parenchyma to vessel elements
-- gelatinous fibers (contact cells)
-- may be hormone-induced or defense mechanism
3

4. 1/13/2010
Tracheid -- more primitive
Tracheary elements
*less specialized state: conduction and support
combined (tracheids)
*more specialized – two lines of specialization
diverged (vessel- conduction; fibers--support)
Decrease in length
Inclined transverse end walls
Scalariform simple perforation plates
Scalariform bordered pitting alternate
bordered pitting
Vessel outline: angular rounded
INCREASED conductive efficiency or safety
Tracheids fiber-tracheids fibers
Going towards mechanical function
4

5. 1/13/2010
Protoxylem differentiates in parts of the Protoxylem
primary plant body that have not compeleted few tracheary elements
their growth and differentiation in monocots, protoxylem lacunae
Metaxylme begins to differentiate in the still Metaxylem
growing plant body but matures after
elongation is completed. wider tracheary elements
Fibers
May be non-functional when plants undergo
secondary growth
5

6. 1/13/2010
Principal food conducting tissue
Transports: sugars, amino acids,
micronutrients, lipids, HORMONES,
FLORIGEN
1. Sieve elements
2. Parenchyma
3. Fibers
4. Sclereids
4
May be present in phloem also:
Laticifers, resin ducts, various idioblasts
6

7. 1/13/2010
Presence of sieve areas (walls with pores) Modified primary pit fields
enucleated Connecting strands– contents of ports
connect protoplasts of neighboring sieve
a. Sieve cells –less specialized
a elements
b. sieve-tube elements or members (only Presece of CALLOSE in each pore
angiosperms) Thicker connecting strands
Ordinary primary pit fields—less thicker
Thin primary wall
Presence of sieve plates
*Sieve plate– wall part bearing sieve areas that
are larger than those on other wall parts of the
same cellll
Protoplasts contain P-protein (slime)
Associated with companion cells
*companion cell
-- specialized parenchyma cells closely related
to sieve tube ontogenetically and functionally
7

8. 1/13/2010
Located at End walls
Simple or compound
Sieve pores are lined with CALLOSE
Callose
-- apparently plays a role in sieve pore
development
Changes in appearance of plastids
stroma becomes less dense; thylakoids are
sparse
Appearance of P protein (eudicots)
P-protein
appears as slime plugs at sieve plates upon
release of pressure when sieve tubes are
severed (sealing of pores of injured elements;
immobilize bacteria)
Unspecialized sieve areas that are similar Derived from the same mother cell as their
throughout the element associated sieve tube elements
No sieve plates Contains many ribosomes, ER, mitochondria,
Elongated and tapering at ends p
plastids
Gymnosperms and vascular cryptogams Nucleus prominent
Informational molecules, ATP , proteins–are
supplied to sieve tube elements
Length of life same as sieve tube members
8

9. 1/13/2010
gymnosperms Gradual localization of highly specialized sieve
Develops from phloem parenchyma or phloem areas to the end walls of elements
ray cells Gradual changes in the position of the endwall
Stain intensely with cytoplasmic stains from very oblique to horizontal
y q
Connected physiologically and Gradual change form compound to simple
morphologically to sieve cells ones
Has connections with sieve cells and lacks Gradual reduction of sieve areas on the side
starch walls of the elements
*specialization direction: root leaf (highly
specialized)
Protophloem
-no companion cells
-sieve tube (ST) elements active for short
period
-sieve areas difficult to distinguish
-obliterated by surrounding cells (ST no
nucleus so not able to divide)
-remaining parenchyma fibers; collenchyma
(leaves)
Metaphloem
- function for many years (plants without
secondary growth)
- longer and wider
- with distinct sieve areas
-companion and parenchyma present
(eudicots; monocots no parenchyma)
- lacks fibers (eudicots
9

10. 1/13/2010
10