Parenchyma which contains air in its intercellular spaces. It helps in aeration and buoyancy. Example: Nymphaea and Hydrilla.

In open vascular bundle, Cambium is present between xylem and phloem. (Stems of Dicots and Gymnosperms).

The endodermal cells which are opposite to the protoxylem elements, are thin walled without casparian strips. These cells are called passage cells. Their function is to transport water and dissolved salts from the cortex to the protoxylem.

(i) They are analogous to companion cells of phloem (Angiosperms).
(ii) They have cytoplasm, nucleus and are: parenchymatous, seen with sieve cells (Phloem) of Gymnosperms.

(i) Guard cells contain chloroplast and can photosynthesize.
(ii) They enclose a cavity/opening which forms the stoma. This helps in gaseous exchange for respiration and photosynthesis.
(iii) The guard cells help in closing and opening of the stoma.

(i) The study of Anatomy helps us to understand I the internal structure of higher plants.
(ii) The organisation of cells and different kinds of tissues is understood by the study of Anatomy.
(iii) It helps to compare the anatomy of different organs of the plant and understand the role of different tissues.
(iv) This field finds application in many fields such as systematics, Forensics and Pharmacognosy.

The pulp of pear contains sclereids because of which it is gritty.

The cells of sclerenchyma & tracheids become dead because they lack protoplasm

S.No. Characters Dicot Stem Monocot Stem 1.  Hypodermis  Collenchymatous  Sclerenchymatous 2.  Ground tissue Differentiated into cortex, endodermis and pericycle and pith Not differentiated, but it is a continuous mass of parenchyma 3.  Starch Sheath  Present  Absent 4.  Medullary rays  Present  Absent 5. Vascular bundles  (a) Collateral and open  (a) Collateral and closed  (b) Arranged in a ring  (b) Scattered in ground tissue  (c) Secondary growth occurs  (c) Secondary growth usually does not occur.

S.No.	Characters	Dicot root	Monocot root
1.	Pericyle	Gives rise to lateral roots, phellogen and a part of vascular cambium.	Gives rise to lateral roots only.
2.	Vascular tissue	Usually limited number of xylem and phloem strips.	Usually more number of xylem and phloem strips.
3.	Conjunctive tissue	Parenchymatous; Its cells are differentiated into vascular cambium.	Mostly sclerenchymatous but sometimes parenchymatous. It is never differentiated in to vascular cambium.
4.	Cambium	It appears as a secondary meristem at the time of secondary growth.	It is altogether absent.
5.	Xylem	Usually tetrach	Usually polyarch

Sclereids (Stone Cells)
Sclereids are dead cells, usually these are isodiametric but some are elongated too. The cell wall is very thick due to lignification. Lumen is very much reduced. The pits may simple or branched. Sclereids are mechanical in function. They give hard texture to the seed coats, endosperms etc., Sclereids are classified into the folowing types.
Types of Sclereids
(a) Brachysclereids or Stone cells:
Isodiametric sclereids, with hard cell wall. It is found in bark, pith cortex, hard endosperm and fleshy portion of some fruits. Example: Pulp of Pyrus.

(b) Macrosclereids:
Elongated and rod shaped cells, found in the outer seed coat of leguminous plants. Example: Crotalaria and Pisum sativum.

(c) Osteosclereids (Bone cells):
Rod shaped with dilated ends. They occur in leaves and seed coats. Example: seed coat of Pisum and Hakea

(d) Astrosclereids:
Star cells with lobes or arms diverging form a central body. They occur in petioles and leaves. Ex: Tea, Nymphae and Trochodendron.

(e) Trichosclereids:
Hair like thin walled sclereids. Numerous small angular crystals are embedded in the wall of these sclereids, present in stems and leaves of hydrophytes. Example: Nymphaea leaf and Aerial roots of Monstera.

Tracheids	Fibres
1. Not much elongated	Very long cells
2. Possess oblique end walls	Possess tapering end walls
3. Cell walls are not as thick as Fibres	Cell wall are thick and lignified
4. Possess various types of thickenings	Possess only pitted thickenings
5. Responsible for the conduction and also mechanical support	Provide only mechanical support

These are primitive type of conducting elements found in Pteridophytes and Gymnosperms. Sieve cells have sieve areas on their lateral walls only. They are not associated with companion cells

Dicot leaf	Monocot leaf
Dorsiventral leaf	Isobilateral leaf
The mesophyll is differentiated into palisade and spongy parenchyma.	Palisade parenchyma is present on both sides of the leaf and spongy parenchyma lies in the centre.
Eg: Sunflower	Eg: Grass.

Fibre	Sclereids
1. Long cells	Short cells
2. Narrow, Elongated pointed ends	Usually short and broad
3. Occurs in bundles	Occurs individually or in small groups
4. Commonly unbranched	Maybe branched
5. Derived directly from meristematic tissue	Develops from secondary sclerosis of parenchyma cells