1. Mature (Permanent) tissues 68 C- Vascular system 68
- Vascular tissues are present in Pterophyta (ferns) and in
Spermatophyta (seeded plants); both divisions are, some-
times, termed as Tracheophyta (plants with vascular sys-
tem formed of tracheae or simply vascular plants).
- Vascular tissues include xylem and phloem tissues.
- Xylem is the water conducting tissue; in addition it acts as
a mechanical support to the different plant organs.
- Phloem is the principal food-conducting tissue of vascular
plants.
- Both vascular tissues form the stele (or vascular column),
they are found (with or without cambium) in vascular bun-
dles (stems) or as separate radial strands (roots),surroun-
ded by the endodermis & pericycle & surrounding the pith.

2. Mature (Permanent) tissues 69 C- Vascular system 69
- Vascular tissues of the primary body are derived from
the procambial strands of the primary meristem situated
below the growing apecies of the shoot or the root or
associated with leaf primordium.
- We will study :
(1) The elements constituting the vascular tissues
(i.e. Xylem & Phloem tissues);
(2) Types of vascular bundles;
(3) Types of stele (or the stelar structure).

3. Mature (Permanent) tissues 105 C- Vascular system 105
The Stele
- Xylem and phloem are found in close association in the
plant body, and together form what is termed the stele
which also includes the pericycle to the outside and the
pith centrally.
Types of steles:
I- Protostele:
- In which the vascular tissue is a single mass in the centre
of the plant organ (i.e. there is no pith) .
- There are 3 different types of protostele:
a- Haplostele: is the simplest type in which the xylem
appears ± circular in cross section, surrounded by
the phloem and there is no pith (e.g. Rhynia « fossil »);

4. Mature (Permanent) tissues 106 C- Vascular system 106
b- Actinostele: in which the xylem may become star shaped
(Stellate), and there is no pith, e.g. Pisalotum.
c- Plectostele: is more advanced than actinostele, where
the xylem is divided into separate plates of which some
are joined and others are, usually, separated by phloem,
and there is no pith, e.g. Lycopodium clavatum.

5. Mature (Permanent) tissues 107 C- Vascular system 107
II- Siphonostele:
- stele of this type has a central column
of pith.
- Various types of siphonosteles are
distinguished according to the position
of xylem and phloem as follows:
(i) Ectophloic sipholostele: the pith is surr-
ounded by the xylem which in turn is surr-
ounded by the phloem so the phloem is
present on the outer side of the xylem only
( e.g. Nicotiana & Salix ).
(ii) Amphiphloic siphonostele: the pith is
surrounded by inner endodermis, inner

6. Mature (Permanent) tissues 108 C- Vascular system 108
pericycle, inner phloem, xylem,
outer phloem, outer pericycle,
and outer endodermis. (common
in ferns, e.g. Adiantum, Marsilea,..).
III- Solenostele :
- This type of stele originates from
either ectophloic or amphiphloic
siphonostele, by the interruption
of the stele with leaf gaps, at long
distances, the cross section above
the position of leaf gap will make
the stele to appear as horse-
shoe-shaped.

7. Mature (Permanent) tissues 109 C- Vascular system 109
IV- Dictyostele:
- This type of stele originates in the same manner as the
amphiphloic solenostele type, however, the stem (or
rhizome) have leaves at short distances, overlap each
other, and this leads to the overlapping of leaf gaps.
- A cross section of such stele reveals the presence of
separate vascular bundles. These vascular bundles are
concentric (central xylem surrounded by phloem, pericycle
and endodermis), called meristeles (e.g. Dryopteris).
V- Eustele :
- This type of stele originates in the same manner as the
dictyostele type, however, form ectophloic solenostele,
instead of amphiphloic solenostele, to produce collateral

8. Mature (Permanent) tissues 110 C- Vascular system 110
vascular bundles (e.g. Dicot stems), arranged in ring .
VI- Atactostele:
- This is a special case of Eustele in which the stele is more
disected with leaf gaps, so that , in transverse section, the
vascular bundles are scattered though the fundamental
tissue (e.g. Monocot stems, Corn & Grasses).

9. Mature (Permanent) tissues 111 C- Vascular system 111

10. Mature (Permanent) tissues 112 C- Vascular system 112
Types of Vascular Bundles
- The term vascular bundle is applied to the separat groups
(strands) of primary vascular tissue.
- On the basis of the orientation of xylem and phloem, the
individual vascular bundles of the stele are classified into:
I- Collateral:
- The xylem & the phloem are at the same radius.
- The xylem tissue lies closer to the center of the axis, and
the phloem towards the periphery of the stem.
- Collateral bundles are characteristic of the stems of Dicots.
and Gymnosperms but also found in Monocots.