Life cycle

Life cycle of  Pinus plant

   Pinus is monoecious plant. Both male and female cones are develop on the same plant.These cones are monosporous. Microspore and micerospoerngia are present on the male cone. Megasporengia and megaspore are produce on female cone.They have no vegetative reproduction in  Pinus. A cycle is show for the regeneration of Pinus plant. A new generation is produced with the cycle. Male cone and female cone are present on the same plant. Male cone is small in size. It produce pollen grains. Female cone is larger in size and produce ovule. Pollen grain reach on the ovule and their cycle start.

Embryo Production
   Diploid nucleus divide thrice and produce eight cell. The lower four cell become proembryonal cells. The upper four nuclei are separated by incomplete cell walls. Four proembryonal divides to produce three tires of cell. Embryonal cell, Suspensor cell and Rosette cell are the three tiers cell of embryo. Embryonal cell. Embryo Cell  The cells of the lower tiers become embryonal cells. The four embryonal cell separate from each other. Each  embryonal cell develop into embryo independently. Embryonal cell forms secondary suspensor cells. The formation of a more than one embryo form a single fertilized oosphere is called polyembroany. Only one embryo is reach maturity. 

   Suspensor cell  The cell of the middle tier become suspensor cells. Suspensor cell elongate very much. It pushes the developing embryos into the prothalial tissue for nurition.  Rosette cell  The cells of the upper tiers are called the rosette cells. These cells do note take part in the development of the embryo. A fully developed embryo is in the form a short straight axis. Its radicle is present towards the micropylar end. Plumule present toward the inner side which is surrounded by the cotyledons. The unutilized tissue of prothalial form endosperm. The persistant nucellus tissues near the micropylar end form the perisperm. The integument become hard testa. Some part of the ovuliferous scale fuses with the development seed. It makes a large wing for dispersal of seed. The axis of the female cone rapidly increase. It produce gaps in ovuliferous scales. The cone become woody.

Seed germination

     The radicle grow out. It splits the testa at the micropyler end. This radicle grows down into the soil and form the primary root. The hypocotyl  elongates to form a loop. Then it become straight. It carries with it the plumule and cotyledons. The testa is also carried up with the cotyledons. The plumule forms the first main shoot. It develops foliage leaves spirally.  Pollination   Each ovule secretes a mucilaginous drop at the micropyler end. A gap is produce between the end of the ovliferous scales. It forms a passage for the entry of pollen grains. Wind carried pollen grains. The mucilage drop entangles the pollen grain. Pollen grain is carried through micropyle to the surface of the nucellus. Fertilization   The pollen grains resumes its activity in the spring. Generative cell divide in to two unequal male cell or sperms. Male cell passes down to the tip of the pollen tube. The pollen tube grows through the nucellus. It passes nucleus fuses with the oosphere to form oospore. The other degenerates. Fertilization us completed in June in next year.