Morphology of Pinus tree

Pinus:

1. A tall, branched tree.

2. Plant body differentiated into root, stem and leaves; tap roots and mycorrhizic roots.

3. Stem cylindrical, branched; the branches are of two types, i. e, branches of limited growth (dwarf shots) and branches of unlimited growth (long shoots).

4. Leaves needle-like and grow on dwarf shoots; no circinate vernation.

6. Resin canals present; no mucilage canals.

7. Root stele diarch to hexarch.

8. Girdle traces absent.

9. Secondary growth; the cambium ring is persistent and produces a continuous cylinder of secondary xylem; annual rings are formed.

10. Mesophyll not differentiated into palisade and spongy tissue; mesophyll cells have peg-like infoldings; two vascular bundles with endarch xylem.

11. Transfusion tissue less developed.

12. No vegetative reproduction.

13. Plants usually monoecious; cones simple and unisexual.

14. Sporophylls arranged in male and female cones.

15. Microsporophyll scaly, not peltate, bearing two microsporangia.

16. Male cones small, grouped in clusters replace the dwarf shoot and not ma

17. Microspores (pollen) winged exine inflated to form balloon-like expans

18. Female cone compact and corresponds to an inflorescence; ovuliferous scale represents female flower.

19. Each megasporophyll or carpel is quite simple; each ovuliferous scale bears two ovules on its upper surface near the central axis.

20. Ovule bears single integument.

22. Pollen chamber and nucellar beak absent.

24. At the time of fertilization the embryosac consists of a gametophyte having many food laden cells bearing 2-3 archegonia.

25. Wind pollination; pollen grains enter the open ovuliferous scale and get entangled in the oozing mucilage drop from micropyle.

28. The microspore cuts off two prothallial cells towards the pointed end (male gametophyte).

30. Male gametes small non-motile.

31. The non-motile sperms are carried to the mouth of archegonia through pollen tube; pollen tube acts as sperms carrier and haustorium.

34. Female gametophyte bears one or two archegonia; no neck canal cell.

36. Usually a time interval of one year in between pollination and fertilization; fertilization occurs in the end of April; pollen tube reaches the neck of archegonium; the neck breaks and receives the contents from pollen tube; male nucleus fuses with the egg nucleus forming oospore.

38. Wall formation starts when eight-nucleate stage is attained.

39. Proembryo has four distinct tiers.

40. Four potential embryos, but only one matures; common occurrence of-cleavage polyembryony.

41. Perisperm present; numerous cotyledons in each seed; no aril; testa dry; endospermic.

42. Seeds winged.

43. Epigeal germination of seed.