Q.3. Describe the structure of dwarf shoot of Pinus with diagram briefly.
Ans. Dwarf Shoot of Pinus: -
The dwarf shoot of Pinus is surrounded by scale leaves. The epidermis is followed by a layer of thick walled cortex (hypodermis) and then by thin walled cortex.
The stellar depends upon the number of needles in which the dwarf shoot terminates. In a trifoliar dwarf shoot there are six conjoint, collateral bundles having endarch xylem. The pith is poorly developed. The vascular bundles are open, showing very limited amount of secondary growth. No annual rings are formed in it.
Q.4. Describe the anatomy of needle of Pinus. (2006)
Related Questions -
Q. With the help of labelled diagrams describe the anatomy of Pinus needle. (2012)
Q. Draw well labelled diagrams of needle of Pinus. (2009)
Ans. The outline of the needle varies in monofoliar, bifoliar, trifoliar and pentafoliar spurs. In a transverse section a needle of trifoliar spur of P. roxburghii appears triangular bifolar spur of P. sylvestris semicircular and a monofoliar spur of P. monophylla circular.
The internal structure of the needle is typically same in all the species of Pinus.
Now we will take the internal structure of the needle Pinus longifolia as seen in transverse section which is as follow.
The transverse section of Pinus longifolia needle shows a triangular outline and its internal tissue may be differentiated outside to inside as follows:
1. Epidermis: -
It is a single layered, thick wall and heavily cutinized with large number of Sunken stomata.
2. Hypodermis: -
It present below the epidermis and consists of one or more layers of fibrous sclerenchymatous cells arranged below the epidermis. Frequently, it is interrupted by the stomatal pits.
3. Mesophyll: -
It present in between the hypodermis and endodermis and is a well-developed tissue. The mesophyll cells are uniform without any distinction into palisade and spongy parenchyma.
The cells of mesophyll are thin walled with small peg like infolding of cellulose projecting in the cavities. These infoldings increase the internal aerating excreting and absorbing surface of the protoplasm. The mesophyll cells also have numerous starch granins and chloroplasts in the mesophyll cells towards hypodermis, few resin ducts (about 3 in P. longifolia) are present. Each resin duct is surrounded by as epithelial layer and a sclerenchymatous sheath.
4. Endodermis: -
It is situated below the mesophyll tissue surrounding pericyle and two central vascular bundled, as a conspicuous layer of large, barral shaped cells which contain casparian strips or bands.
5. Pericycle: -
It lies internal to endodermis and is multilayered. Within the pericycle are two vascular bundles. In the case of Pinus longifolia pericycle is slightly complex and is made up of different types of cells which are as follows:
(i) Parenechymatous Cells: The pericycle is largely composed of thin walled cells.
(ii) Sclerenchymatous Cells: They are in the form of a T-shaped girdle over arching and separating two vascular bundles of the needle.
(iii) Albuminous Cells: They are found abutting on the phloem tissue of the bundles. They are thin walled cells richly supplied with protiens and starch.
(iv) Trachiedal Cells: There are tracheid-like cells having pits, found close to the xylem elements of the bundles. This is generally referred to as transfusion tissue.
6. Vascular Bundles: The vascular bundles are two in number, they are collateral and embedded in many layered pericycle. The xylem in each bundle in Pinus longifolia faces the pointed inner surface while in P. sylvestries xylem is facing towards the upper flat surface.
Physiological Functions of Various Parts
The leaf of Pinus shows xerophytic characters and various parts are adopted for this purpose.
Epidermis: Thick walled epidermis covered by a highly developed cuticle and sunken stomata reduce the rate of transpiration.
Hypodermis: The thick hyppodermis is also cuts down the rate of transpiration.
Transfusion Tissues: The transfusion tissues of the pericyle help in the movements of the nutritive solution. The trachedial cells carry inorganic solution from the xylem to mesophyll while albuminous cells carry the organic compounds from the mesophyll to pholem.
