cupressus.pptx

Cupressus morphology anatomy and reproduction

1. Cupressus

2. SYSTEMATIC POSITION Division: Pinophyta Class: Pinopsida Order: Pinales Family: Cupressasceae Genus: Cupressus

3. Occurrence They are evergreen trees or large shrubs growing to 5- 4 m tall. These are native to scattered localities in mainly warm temperate regions in the Northern Hemisphere. All have decorative merit, particularly in a young state. Common species planted in the plains and hills of India include: C. funebris , C.cashmeriana , C.sempervirens .

4. Morphology Tree is evergreen, large (5-40m ) tall, with pyramidal appearance. The bark is thin, fibrous and greyish brown and peel off in long strips. Branching is of 2 types: horizontal or erect main branches, which are spirally arranged on the main stem and drooping side branches. Main branches are devoid of leaves, whereas the drooping branches bear small, greyish-green opposite and decussate leaves adpressed to the axis. The leaves of the lateral pair are folded face to face and those of the facial pair are flattened and grooved in the middle . 2 types of leaves are seen : The leaves of the apical zone are small, closely placed with acute apex and serrated margin. Mature leaves are longer, brownish and distantly placed due to elongation of the internode. The leaves are characterized by a prominent midrib and scattered stomata on both the surfaces.

5. The male cones (6-7mm long) , borne terminally on pendulous branch, are brownish when mature. 6 to 8 pairs of microsporophylls , each bearing 2 to 6 sporangia abaxially , are arranged in a opposite and decussate manner on the cone axis. The female cones (10-12 mm long) are axillary on the pendulous branches and each consist of four pairs of seed scale complexes arranged in a opposite and decussate manner. The lower most pair is generally sterile. The fertile scales are peltate bearing 3-7 ovules/seeds per scale. The fertile seed scales complexes are thick, four to six sided and have a central pointed process called the boss. The mature cone is brown and woody and persists on the tree long after the seed shed. The seed are dark brown , orbicular, compressed and narrowly winged. The wings of successive seeds overlap.

6. ANATOMY STEM Both cortex and pith are narrow and consist of parenchymatous cells in young stem. After Secondary growth, distinct annual rings are formed. Xylem Cylinder is thicker than the periderm, cortex and secondary phloem. Secondary phloem is composed of sieve elements, phloem parenchyma, phloem fibres and resin ducts. Sieve areas are confined to the radial walls. The resin canals are large, bounded by 2 or 3 layers of secertory cells. Phloem fibres occur at regular intervals in single tangential layers. These alternative with rings of parenchyma and resin cells. The phloem rays are uniseriate and 4 or 5 cell high . These are thin walled with simple pits . The tracheids of Secondary xylem are long and narrow with circular to elliptical bordered pits on their radial walls.

7. In the tracheids of summer wood , tangential pitting is also seen. Parenchymatous cells are resinous. Xylem rays are uniseriate , 1-5 cells high, comprising parenchymatous cells and showing simple pits. The wood is devoid of resin canals. Thd pith get obliterated and is seen as a dense region in the centre .

8. LEAF Epidermis is covered with a thin cuticle. Single-layer of thick walled cells constituting the hypodermis which may be discontinous at places. Mesophyll is differentiated into a layer of elongated palisade cells and spongy parenchyma. The palisade cells are towards the abaxial side or lower surface and contain abdundant chloroplast. The spongy tissue is composed of large irregular cells with numerous intercellular spaces. This is single vascular bundle with a resin canal below it.

9. REPRODUCTION Microsporangium & Microsporogensis Microsporangia arise on the abaxial side of the microsporophyll. Below the epidermis few hypodermal archesporial cell differentiate which divide periclinally to give rise to primary perietal layer and primary sporogenous cells. The former after division forms the middle layer towards outside and tapetum towards inside. Primary sporogenous cells divide in all planes to form sporogenous tissue, the last cell generation of which eventually give rise to MMC. MMC undergo reduction division followed by cytokinesis which is simultaneous.

10. The microspore tetrads are isobilateral and tetrahedral. A young microspore has a large nucleus, dense cytoplasm and numerous dtrach grains. The pollen grains are shed at the uninucleate stage. No prothallial cells ate formed. Pollen wall consist of a fine granular, thin exine and a thick uniform intine . Pollen are non-winged Prior to meiosis , the strach grains which were present at the periphery get distrubuted throughout the cytoplasm of the microspore mother cell. After meiosis 1 the strach grains get divided in 2 groups and after meiosis 2 four ssuch groups are seen. There is thus a equal distribution of strach in the 4 microspore.

11. MALE GAMETOPHYTE The wind dispersed pollen grains are caught in the pollination drop and sucked in reaching nucellus . The micropylar canal which is very wide during pollination is closed after pollination by the repeated division of the cells of the inner layer. Also the edges of the seed scales complex give out teeth-like appendages which closely interlock with each other. The pollen grains are aporate and germinate on the nucellar tip . At the time of pollen germination , the exine is thrown off after it gets ruptured irregularly. The microspore divides to form a small lenticular antheridial cell and a large tube cell.

12. The tube nucleus moves into the pollen tube followed by the antheridial cell which divides to give rise to a large spermatogenous cell and a stalk cell. The stalk cell soon loses its wall and comes to lie near the tip of the pollen tube along with the tube nucleus. Just before the pollen tube reaches the archegonium the tube and the stalk nuclei degenerate and spermatagenous cell divides into 2 equal male cells. Multiple male gamates have been reported. The multiple male cells are produced by the super numerary division of the spermatogenous cells.

13. MEGASPORANGIUM & MEGASPOROGENESIS The ovules are unitegmic and crassinucellate . Several deep-seated sporogenous cells have been reported. The megaspore mother cell after meiosis gives rise to linear tetrad of megaspores. Some times 2or more megaspore may start enlarging , but these become arrested soon.

14. FEMALE GAMETOPHYTE Nuclear divisions in the early stages are Simultaneous. The gametophyte become cellular through alveoli formation. A very conspicuous spongy tissue comprising 2or 3 layer surrounds the free nuclear gametophyte. It is derived from the non-functional sporogenous cells. Few cells at the micropylar end of the female gametophyte become prominent and differentiate into archegonial initials. They divide transversely to give rise to a small neck initials and a large central cell. The neck is made up of 8 cells arranged in 2 tiers of four cells each. The central cell divides to form an ephemeral ventral canal nucleus and a egg nucleus. The latter enlarges and comes to lie in the centre of the devolping archegonium .

15. A mature archegonium is oblong othe elongated a large egg nucleus , a ventral canal nucleus and eight neck cells. The archegonia occur in archegonial complexes. A group of archegonia is surrounded by a common jacket. With the development of the archegonial complex, the adjacent gametophytic tissue grows upward, resulting in the formation of an archegonial chamber. The total number of archegonia is 10-13. The archegonia differentiate in that region where the pollen tubes make contact with gametophyte. The archegonial complexes are terminal at the micropylar end.

16. FERTILIZATION After traversing the nucellus , the pollen tube arrives in the archegonial chamber and releases the male cells. Subsequent to the degeneration of neck cells, a passage is formed through which the male cells enter the archegonium . Generally only one male cell finds its way into an archegonium . The male nucleus is thus surrounded by its middle and inner cytoplasmic zones while moving through the egg or maternal cytoplasm. As it reaches the egg nucleus, the male nucleus moves in advance of the cytoplasmic sheath. The two fusing nuclei make contact with each other and take a turn of 180° so that the male nucleus comes to lie below the egg nucleus.

17. The two inner zones of the male cytoplasm envelope the zygote and later become incorporated into the neocytoplasm . After the fusion of the nuclear membrane , the zygote is formed surrounded by the neocytoplasm , the egg cytoplasm having degenerated.

18. EMBRYOGENY The zygote nucleus divides thrice to give rise to 8 free proembryonal nuclei at the archegonial base. Wall formation take place resulting in primary proembryo comprising 2 tiers of 4 cells each.( Primary upper tier and Primary embryonal cells) The primary upper tier again divides transversely to form an upper open tier and a middle suspensor tier. The primary embryonal cells also divide to form embryonal cells resulting in a 16- celled secondary proembryo . The cells of suspensor tier elongate to push the embryonal tier deep into the gametophytic tissue. Each cell between the terminal embryonal cell and suspensor elongates forming embryonal suspensor.

19. Both simple and cleavage polyembryonal are common. The apical embryonal cells divides in all planes to form a meristamatic tissue. The shoot apex and the root apex are differentiated by the activity of cells at proximal end and distal end , respectively. The cells between the root and shoot apices elongate along the long axis of the embryo. In peripheral region of the shoot apex , a group of cells become active and divides more rapidly than the rest resulting in 2- well developed cotyledons.