Pinus -External Morphology,Internal Structure and Reproduction

                             Pinus

External morphology :-

Root :-   

The tree has a well developed tap root system .

When the plant is growing on a shallow soil in the hills ,the lateral roots spread very wide to fix the plant firmly into the plant firmly into the  soil.

Pinus Morphology

Roots make association with fungi in the soil called mycorrhizae.it is kind of symbiotic association where the fungud does not affect the plant root bt provide soil nitrogen and phosphate and other minerals from root to the root .

Stem :-

 Stem is woodly and branched .the lower unbranched part of the stem is called Trunk .

(1)   Branch of limited growth

(2)   Branch of unlimited growth .

The branch is excurrent where the terminal bud or main stem shows more growth than the terminal buds of lateral branches .lateral branches  grow out from the main stem and are so disposed that the plant gives a conical appearance .

Dwarf Shoots are  small a few mm. long and are dot like .They arise in the axial of a scaly leaf  on the long shoot .

Green leaves occur on the dwarf shoots only .they also have scaly leaves  on them .

Leaves :-

 Leaves are of two types :-

(a)   Foliage leaf :-

   There    leaves are long narrow ,green and look like needles .

They occur in groups of 2-5 in different species on the tip of dwarf shoots the dwarf shoot along with needles is also called a spur .

(b)   Scaly leaves :- 

They are small brown and membranous .

Scale leaves occur on both long shoot as well as on dwarf shoots . 

They are decious .However ,They are protective and retain moisture around the stem.

Internal Structure :-

T.S. Young Root:-

 1. Outermost layer of the circular roots is thick-walled epiblema with many root hair.

Young Root of Pinus 

2. Epiblema is followed by many layers of parenchy­matous cortex.

3. Inner to the cortex is present a layer of endodermis and many layers of pericycle.

4. Vascular bundles are radially arranged and diarch to tetrarch with exarch protoxylem.

5. Protoxylem is bifurcated (Y-shaped) towards the periphery, and in between each bifurcation is present a resin cannal .

6. Phloem is present alternate to the protoxylem.

7. Pith is poorly-developed or absent.

T.S. Old Root Showing Secondary Growth:-

1. On the outer side are present a few layers of cork, formed by the meristematic activity of the cork cam­bium.

2. Cork cambium cuts secondary cortex towards inner side.

3. Many resin canals and stone cells are present in the secondary cortex, the cells of which are sepa­rated with the intercellular spaces.

4. Below the phloem patches develop cambium, which cuts secondary phloem towards outer side and sec­ondary xylem towards inner side.

5. Crushed primary phloem is present outside the sec­ondary phloem .

6. Many uniseriate medullary rays are present in the secondary xylem.

7. Primary xylem is the same as in young roots, i.e., each group is bifurcated (Y-shaped) and a resin canal is present in between the bifurcation.

Long Shoot (Young):-

1.      Many leaf bases are present on the stem , due to which it appears wavy in outline.

Young Shoot

2.       Outermost single-layered, thick-walled epidermis is heavily cuticularized and followed by multilayered cortex.

3.       A few outer layers of cortex are sclerenchymatous, and some inner layers are parenchymatous.

4.      In the inner layers of cortex are present many resin canals.

5.      The stele is eustelic or polyfascicular endarch siphonostele.

6.       Vascular bundles are conjoint, collateral, open and endarch, and resemble greatly with that of a dicot stem. 5-10 vascular bundles are arranged in a ring.

7.       Endodermis and pericycle are indistinguishable.

8.       Narrow xylem rays connect the cortex and pith.

9.       Endarch xylem consists of only tracheids.

10.      Phloem is present on the ventral side and consists of sieve cells, sieve plates, phloem parenchyma and some albuminous cells.

     11.      Intrafascicular cambium is present in between the xylem and phloem.

     12.     Many leaf traces are also present.

      13.     A small parenchymatous pith is present in the cen­tre of stem.

T.S. Needle (Foliage Leaf):-

 1.  It is circular in outline in Pinus monophylla, semi­circular in P. sylvestris and triangular (Fig. 38) in P. longifolia, P. roxburghii, etc.

Foliage Leaf

2.  Outermost layer is epidermis, which consists of thick-walled cells. It is covered by a very strong cuticle.

3. Many sunken stomata are present on the epider­mis.

4. Each stoma opens internally into a substomatal cavity and externally into a respiratory cavity or vestibule.

5. Below the epidermis are present a few layers of thick-walled sclerenchymatous hypodermis. It is well-developed at ridges.

6. In between the hypodermis and endodermis is present the mesophyll tissue.

7. Cells of the mesophyll are polygonal and filled with chloroplasts. Many peg-like infoldings of cellulose also arise from the inner side of the wall of meso­phyll cells.

8. Few resin canals are present in the mesophyll, adjoining the hypodermis. Their number is vari­able but generally they are two in number.

9. Endodermis is single-layered with barrel-shaped cells and clear casparian strips.

10. Pericycle is multilayered and consists of mainly par­enchymatous cells and some sclerenchymatous cells forming T-shaped girder, which separates two vascular bundles .

Transfusion tissue con­sists of tracheidial cells.

Reproductive Structures of Pinus:-

1. Plant body is sporophytic.

2. Pinus is monoecious, and male and female flowers are present in the form of cones or strobili on the separate branches of the same plant.

3. Many male cones are present together in the form of clusters, each of which consists of many microsporophylls. The female cones consist of megasporophylls.

4. The male cones on the plant develop much earlier than the female cones.

Male Cone:-

Separate a male cone from the cluster, study its struc­ture, cut its longitudinal section, study the structure of a single microsporophyll, and also prepare a slide of pollen grains and study.

1.      The male cones develop in clusters  in the axil of scaly leaves on long shoot.

Male Cone

2.       They replace the dwarf shoots of the long shoot.

3.       Each male cone is ovoid in shape and ranges from 1.5 to 2.5 cm. in length

4.      A  male cone consists of a large number of microsporophylls arranged spirally on the cone axis.

5.      Each microsporophyll is small, membranous, brown-coloured structure.

6.       A microsporophyll (Fig. 41) is comparable with the stamen of the flower of angiosperms because it consists of a stalk (=filament) with a terminal leafy expansion (= anther), the tip of which is projected upwards and called apophysis.

7.      Two pouch-like microsporangia (= pollen sacs) are present on the abaxial or undersurface of each microsporophyll. In each microsporangium are present many microspores (= pollen grains).

8.      Each microspore or pollen grain is a rounded and yellow-coloured, light, uninucleate structure with two outer coverings, i.e., thick outer exine and thin inner intine .

9.      The exine protrudes out on two sides in the form of two balloon-shaped wings. Wings help in floating and dispersal of pollen grains.

10.   Wings help in floating and dispersal of pollen grains.

11.   A few microsporophylls of lower side of cone are sterile. Sporangia are also not present on the adaxial surface of each microsporophyll of the male cone.

Female cone:

Observe the external features and longitudinal sec­tion of a young female cone and also study 1st year, 2nd year and 3rd year female cones.

1.      Female cone develops either solitary or in groups of 2 to 4.

2.      They also develop in the axil of scaly leaves on long shoots like male cones.

3.      Each female cone is an ovoid, structure when young but becomes elongated or cylindrical at maturity.

L.S. Female Cone:-

 1. Many megasporophylls are arranged spirally on the cone axis.

3. A few megasporophylls, present at the base and at the apex of strobilus, are sterile.

4. Megasporophylls present in the middle of the stro­bilus are very large and they decrease in size to­wards the base and apex.

Female cone

5. Each megasporophyll consists of two types of scales, known as bract scales and ovuliferous scales.

6. Bract scales are thin, dry, membranous, brown- coloured structures having fringed upper part. These are also called carpellary scales.

7. An ovuliferous scale is present on the upper sur­face of each bract scale.

8. Each oruliferous scale is woody, bigger and stouter than bract scale and it is triangular in shape. A broad sterile structure, with pointed tip, is present at the apex of these scales. This is called apophy­sis.

9. At the base of upper surface of each ovuliferous scale are present two sessile and naked ovules.

10. Micropyle of each ovule faces towards the cone axis.

11. Each ovule is orthotropous, and it remains sur­rounded by a single integument, consisting of an outer fleshy, a middle stony and an inner fleshy layer. It opens with a mouth opening called micro­pyle.

12. Integument surrounds the megasporangium or nucellus.

13. Just opposite the micropyle is present a pollen chamber.

14. In the endosperm or female gametophyte are present 2 to 5 archegonia.

Female Cone of 1^st Year :-

 It is oval  in shape.

2. It ranges from 1 to 4 cm. in length.

3. It is green to reddish-green in colour.

4. It is attached with the help of a short stalk on the long shoot.

5. Megasporophylls are arranged very close to each other, and so the cone is a compact structure.

Female Cone of 2nd Year:-

1. It is elongated and larger than the first year cone.

2. It ranges from 5 to 15 cm. or more in length.

3. It is red-coloured structure.

4. It is woody in nature.

5. Megasporophylls are compactly arranged ,but not so compact as in 1st year cone.

6. Seeds are present inside in the later stages

Female Cone of 3rd Year :-

1. It is elongated or roughly rounded in shape.

2. It is also woody in nature like the 2nd year cone.

3. Megasporophylls  are loosely arranged.

4. Seeds are dispersed from 3rd year cone.