Pinus - Class 11 PDF Download

Kingdom   → Plantae

Sub kingdom →   Embryophyta

Division →     Tracheophyta

Class      →     Gymnospermae

Subclass →    Coniferophyta

Order     →   Coniferales

Family   →   Pinaceae/Abitaceae

Genus    →   Pinus

Species Of Pinus

• There are six species of Pinus commonly found in India

(i)   Pinus gerardiana – (Chilgoza Pine) 

(ii)  Pinus wallichiana Syn. Pinus excelsa – (Blue Pine/Kail) 

(iii) Pinus roxburghii Syn. Pinus longifolia – (Chir Pine) 

(iv) Pinus merkusii (Teenasserim Pine) : Height-3 mt

(v)  Pinus insularis Syn. Pinus khasya – (Khashi Pine) 

(vi) Pinus armandi (Armandi's Pine)

• Pinus is a evergreen and perennial tree with xerophytic adaptation which is growing on the slopes of hills in temperate climate. It is conical in shape due to excurrent growth of the plant.

Note : The excurrent/conical habit of Pinus tree is caused by auxin effect on the growth of stem tip & axillary branches

External Morphology Of Pinus

1. Main plant body of Pinus is sporophytic and which is differentiated into root, stem and leaves.

1.   Root : Well developed tap root system is found in Pinus. Root hairs are poorly developed. Ectomycorrhiza are present.

• Basidiomycetes fungus like Clavatia, Scleroderma, Amanita and Boletus etc. are present in mycorrhiza in the form of symbiont in root of pinus. They help in absorption of water and minerals.

2.   Stem :

• Stem of the Pinus is erect/straight, cylindrical, long, woody and branched.
• Branches are monopodial and developed from the axis of scaly leaves which are present on the stem. Branching gives conical appearance to plant.
• Branches are Dimorphic.

(i)   Long Shoot : 

• These are developed in the axis of scaly leaves on stem after the growth of every year. In long shoot, apical bud is found. These are responsible for unlimited growth.
• These branches bear only scaly leaves.    

(ii)  Dwarf Shoot/Branches of limited growth or Brachyblast :

• They develop in the axis of scaly leaves on the long shoot and bear both scaly and foliage leaves.
• They possess foliage leaves at their apex.
• These branches do not have apical bud and hence show only limited growth.
• A dwarf shoot with a group of needle like foliage leaves, called as foliar spur.

3.   Leaves : 

• The leaves are Dimorphic.

(i)   Scaly leaves      
(ii)  Foliage leaves/Photosynthetic leaves.

(i)   Scaly leaves : 

• The scaly leaves are dark brown, membranous, thin and small, and present on both long and dwarf shoots.
• They do not help in photosynthesis

Main function : protection of the young buds.

• They fall off as the branches are mature.
• The scaly leaves on the dwarf shoots have a distinct midrib and they are called Cataphylls.

(ii)  Foliage leaves : (or photosynthetic leaves)

• They develop only on the dwarf shoot and present on their apex.
• The foliage leaves are green & needle like.

Note : The foliage leaves are Photosynthetic and remain persistent for several years. The needle like nature of the foliage leaves indicates xerophytic adaptation.

Internal Structure Of Pinus

(A) Internal Structure Of Root :

1. Internal structure of primary root of Pinus is similar to dicot root, but vessels in xylem and companion cell in phloem are absent.

 (B) Internal Structure Of Pinus Stem.

1. The internal structure of Pinus stem is similar to that of a dicotyledon stem.

1.   Vascular Bundles : 5-9 Primary Vascular Bundles are presents. They are arranged in a ring. The vascular bundles are conjoint, collateral, Open & endarch. The protoxylem tracheids possess spiral thickening where as metaxylem tracheids have reticulate thickening.

Note : In transverse section of the stem (long shoot) appears wavy or irregular in outline due to the presence of close appressing scaly leaves and dwarf shoots.

1. Leaf of the pinus is xeromorphic. Outline of the T.S. section of Pinus leaf (Needle) depends upon number of foliage leaves on foliar Spur :

1.  Epidermis : The single layered epidermis consists of heavily cutinized thick walled cells. It has many sunken stomata. Each stomata consists of two guard cells and 6-9 subsidiary cells. Stomata are present on both surface.

2.   Hypodermis : It is more than one layered and composed of sclerenchymatous cells. Due to the presence of substomatal cavities. Hypodermis is discontinuous.

• In P.longifolia, the hypodermis is more developed at the corners.

3.   Mesophyll : Mesophyll (3 – 5 layered) is made up of parenchymatous cells. Large number of long peg like process are formed by infolding of internal cell well of mesophyll. So it is known as "armed mesophyll". It increases the photosynthetic area of leaf. Leaf mesophyll is not differentiated in it.  

4.   Endodermis : It is made up of barrel shaped cells. Casparian thickening are present on their radial wall.

5.   Pericycle : A multilayered pericycle is present next to endodermis. It consists of the following types of cells.

(i)   Parenchymatous cell :  Most of the pericycle is composed of parenchymatous cells which are densely filled with starch grains.

(ii)  Albuminous cell : These cells occur in close contact with the phloem cells. They are also parenchymatous cells which are packed with proteins and starch grains. They do not possess pits and probably helps in translocation of nutrients from mesophyll to phloem cells.

(iii) Tracheidial cells :  These are tracheids like cells which occur close to xylem cells. These cells possess pits & helps in conduction of water & minerals from xylem to mesophyll cells.

Albuminous cell + Tracheidial cell - Transfusion tissue

(vi) "T" Shaped sclerenchymatous girdle

6.   Vascular Bundle  :

• In the middle of the leaf two vascular bundles are surrounded by bundle sheath. Vascular bundles are conjoint, collateral, Open & endarch. "T' shaped girdle is found between the both vascular bundls. 'T' shaped girdle is composed of sclerenchymatous cells.

• Pinus needle →  Amphistomatic
• Stomata – Haplochelic type. i.e. subsidiary and guard cells are arises from separate cells.
• The needle possesses basal meristem which helps in their elongation

• Linear uniseriate bordered pits are present in tracheids
• Clear annual ring is found in Pinus.
•  Resin canals are also found in secondary xylem.

Important Point :

1. An important characteristics features of Pinus wood is the presence of bars of Sanio. They occur in the form of crescentic bars in between the bordered pits.
2. These bars are formed by the deposition of cellulose & pectin on Tracheidial walls.

Reproduction In  Pinus    

1. Pinus is a Sporophytic & heterosporous plant. The plant body forms two types of spores i.e. microspores and megaspores. The spores are haploid which indicate the first cell of gametophytic phase.
2. The plants are monoecious and male & female cones are formed on different branches of the same plant. It means it is a autoicous plant.
3. Male & female cones are monosporangiate.
4. Exception : In Pinus roxburghii, P. montana and P. maritima the cones are bisporangiate. i.e. cone possess two types of sporangia.

Male Cone :  

1. Male cone are developed in the axis of scaly leaves on the branches of unlimited growth in place of dwarf shoot. The male cones are considered as modified dwarf shoot. They are develops in groups, just behind the apical bud on the branches of unlimited growth. Thus main shoot continues to grow further. The number of cones in a cluster varies from 15 (Pinus wallichiana) to 140 (Pinus roxburghii).

Structure Of Male Cone :  

1. Each male cone is small & oval shaped structure about 2-4 cm long, 5-6 mm in diameter and 60-150 micro sporophylls are arranged spirally on the central axis of each male cone. Each micro sprophyll is a membranous, stalked & roughly triangular structure. (microsporophyll Compared with stamen of angiosperm)
2. The apical sterile part of the micro sporophyll is known as apophysis. It bears two microsporangia at the base of its abaxial side. Each micro sporangium has numerous microspores.
3. Microsporophylls are arranged at right angle to the cone axis in such a manner that the apophysis of the upper micro sporophyll is overlapped by the apophysis of the lower microsporophyll.
4. Development of microsporangium : - Eusporangiate type.

Structure Of Microspore :       

      (i)   Exine : This layer is highly cutinized and it is found only at one side.     

      (ii)  Exointine : Two wings are developed on lateral side of this layer of microspore. It is a part of exine.

      (iii) Intine  : It is inner most layer of microspore.

Development Of Male Gametophyte :   

1. The microspore is the first cell of the male Gametophyte. The Germination of microspore starts in situ i.e., they germinate while still inside the microsporangium.
2. The microspores are released from the microsporangium after partial development of male gametophyte. The rest of the development of male gametophyte takes place in the pollen chamber of the ovule after pollination.  

(A) Development of male gametophyte within the microsporangium before pollination :

Pollination : Pollination takes place through the air at 4-celled stage. In India, dehiscence of microsporangium takes place in warm & dry environmental conditions.

1. The microspores are released in such a large quantity that pine forest appears yellow at the time of dehiscence of microsporangium. This is called "shower of sulphur".

     
(B) Development of Male Gametophyte after pollination :

• After pollination the 4-celled male gametophyte reaches to the pollen chamber and there it remains inactive for about 11 months. (The ovuliferous scale during this period have thickened and closed the cone completely. The ovule is not yet ready for fertilization.) Further development of the male gametophyte starts in the next spring.
• Exointine breaks off from the middle of the wing and the tube cell comes out in the form of pollen tube. Pollen tube reaches to archegonia through nucellus.
• Pollen tube is rich with starch grains & it may be branched or unbranched. It acts as a sperm carrier. Tube nucleus moves into the pollen tube while the generative cell remains inside the pollen grain.
• The generative cells of the 4-celled gametophyte divide to form a body cell and a stalk cell. The nucleus of the body cell divides to form two nuclei just before fertilization. The male nuclei function as sperm which is microscopic, non-flagellate & ephemeral structure.
• Thus mature male gametophyte of Pinus is 6-celled.  

FEMALE CONE :  

1. Female cones are developed on long shoot in place of dwarf shoot. Female cones are also called as modified dwarf shoot.
2. The female cone are formed in groups (1-4 in each group), in the axis of the scaly leaves towards the tips of long shoots of the current year. The female cone with seed takes about three year to mature.
3. The female cones are much larger than the male cones. They are usually 15-20 cm long.
   [Pinus coultre = 25-35cm & Pinus lambertiana =  60 cm]     

STRUCUTRE :    

1. Some basal megasporophylls are small & sterile & the rest are fertile. The megasporophyll is a compound structure, consisting of two types of scales : -

(A) Bract scale
(B)  Ovuliferous scale    

(A) Bract scale :

• It is small membranous structure which is directly attached to the cone axis just below the ovuliferous scale. At the maturity of cone, the bract scale curve inwards so that seeds are dispersed easily.  
• Each bract scale has a single vascular bundle with its xylem pointing upwards.

     
  (B) Ovuliferous scale :

• It is thick, large woody and brownish structure, attached to the dorsal surfaces of the bract scale.
• It is roughly triangular in shape and its upper broad and thick part is known as apophysis. Two ovules are present at the base of the ovuliferous scale on its dorsal surface.
• The micropyle of each ovule is directed towards the cone axis.

STRUCTURE OF OVULE :

1. Ovule of pinus is anatropous, unitegmic & sessile. The following part can be seen in longitudinal section of the ovule.

(i)   Nucellus : It is the massive parenchymatous region of the ovule.

(ii)  Integument : It is the thick protective covering around the nucellus. It has a very narrow aperature at the apex of the nucellus. It is known as micropyle.  

The integument is differenciated in to three layers.

(i)   Outer fleshy layer       
(ii)  Middle stony layer   
(iii)  Inner fleshy layer.

(iii) Pollen chamber : A small furrow is present opposite to the micropyle in the nucellus region which is known as pollen chamber. Material secreted by nucellus is found in this chamber during pollination which is known as "Pollen drop".

• Endosperm & Archegonia are present in the centre of nucellus region.

Megasporogenesis : 

1. At the apex of nucellus (towards micropyle), hypodermal cells is differentiated from other cells by its larger size, called as archesporial cell. Archesporial cell divides by periclinal division to form an outer primary parietal cell & inner sporogenous cell. Sporogenous cell function as a megaspore mother cell. Megaspore mother cell divide meiotically to form a linear tetrad of megaspore. Out of four, three megaspore degenerate which lies towards the micropyle. Only one megaspore remains functional which is present towards the chalazal end.  

Development Of Female Gametophyte :, 

A.  Development Of Endosperm :

• Functional megaspore first of all increases in size then after free nuclear division take place in nucleus of functional megaspore resulting 2000-2500 nucleus are formed. All the nucleus move towards the periphery due to vacuole formation in center.
• There is one characteristic feature of Pinus, in which long multinucleated tube-like cells are developed radially in early stage. These are known as alveoli. Later on uninucleated cells are formed due to the formation of walls. The structure is known as endosperm.
• Endosperm is haploid structure because it is derived from the megaspore before fertilization.
• The nucellus cells surrounding the endosperm form a 2-3 layered nutritive layer. This layer is known as spongy layer or endosperm jacket & it is equivalent to the tapetal layer.

B.   Archegonia :

• 2-5 archegonia (normally two) are formed towards the micropylar end in female gametophyte.
• Each archegonium at maturity consists of eight neck jacket cells arranged in two tiers of four each and a venter having a small venter canal cell and large egg cell. Neck canal cells are absent. The venter canal cell disorganizes before fertilization.
• A nutritive layer is differentiated around the central cell & this layer is known as archegonial jacket. The jacket helps in conduction of nutrients from the endosperm to the archegonium.
  Note : - P.roxburghii and P.wallichiana 4-4 neck cells & in Cycas archegonium 2-4 neck cells are found in the neck region.

1. Fertilization is siphonogamous. The process of fertilization takes place after the 12-14 month of pollination.
2. Many archegonia fertilized in a female gametophyte but only one zygote is able to form an embryo successfully.

Development Of Embryo : 

1. Meroblastic (embryo is formed by only a part of oospore) and endoscopic (development of embryo takes place inside the megasporangium directed away from micropyle)
2. Development of embryo can be studied in the following two steps.
   (A) Development of proembryo (16-celled) from zygote
   (B) Development of embryo from proembryo

(A) Development of proembryo from zygote :

• Pinus proembryo consists of 16 cells arranged in four tiers.

(i)   Nutritive tier : The upper most tier consisting of incomplete cells is known as nutritive tier and it provides nutrition.

(ii)  Rosette tier : Function conduction of nutrient between embryo & suspensor.

(iii) Suspensor tier : The cells of the suspensor tier elongate to form suspensor. Its cells are long which pushed the embryo into the endosperm.

(iv) Embryonal tier : The lower most tier is known as the embryonal tier; its cells divide to form embryo.

(B) Development of embryo from proembryo : 

• All the four cells of the suspensor tier elongate considerably and as a result the embryonal cells present at their base are embedded in the endosperm.
• Due to the limitation of space in the endosperm, the primary suspensor cells become coiled to each other.
• At this stage, the cells of the embryonal tier divide by transverse division and form another tier of cells, known as embryonal tubes or secondary suspensor.   
• The cells of the embryonal tier separate from each other and form four independent embryos. The phenomenon of the formation of more then one embryo from zygote is known as polyembryony.   
• In pinus, as the polyembryony occurs by the splitting of a zygote. It is known as cleavage polyembryony.
• Another type of polyembryony found in pinus is simple polyembryony (when more than one embryo is developed as a result of fertilization of different archegonia.)

Structure Of Embryo 

(i)   Cotyledons : Usually more than two (3 to 18)

(ii)  Plumule or Shoot apex : Present between the cotyledons in the opposite direction of the micropyle.

(iii) Radicle : Directed towards the micropyle 

1. Hypocotyl : Present in between the plumule & radicle.

Parts Of Ovule

Parts of Seed

(1) Integument – 

(i) Outer fleshy layer –  Disappear

 (ii) Inner fleshy layer  –  Tegmen is formed in the form of thin layer

(iii) Middle stony layer  –  It forms the outer most covering of the seed called testa.

(2) Nucellus    –  Present in the form of thin layer which is known as "perisperm".

(3) Micropyle  –  On the apex of seed in the form of a pore.

(4) Thin layer of Adaxial   –  surface of ovuliferous Scale

Forms wing of seed.

• The mature seed represents three generations –

1. Old sporophyte       – Testa, tegmen and nucellus
2. Gametophyte  – Endosperm (female gametophyte)
3. New sporophyte     – Embryo

Germination of seed :

      "Epigeal" type of germination is found in seed of Pinus i.e. cotyledon come outside on the soil surface by elongation of the hypocotyl.

1. The wood of P.roxburghii (Chir) and P.wallichiana (Kail) is an important timber. It is suitable for making railway sleeper, packing cases, furniture, etc Besides, it is also used for making matchsticks.
2. Pinus roxburghii, P. wallichiana, P.insularies and P.merkusii are the chief sources of turpentine in India. Rosins, obtained as a residue after the distillation of pine resin, are used in paper sizing, varnish making enamels and in the preparation of plasters and ointments.
3. The roasted seeds of P.gerardiana (Chilgoza pine), P.edulis and P.monophylla are edible.