Oct 1, 2009

Reproduction in Pinus

At every season, Pinus tree reproduces reproductive structures called cones. Cones are of two kinds, male and female cones. Both male and female cones are produced on the same tree but on different branches.

Male cones are usually 1 cm or less in length. They are much smaller than the female cones. On male cones, there are spirally arranged leaves like structures called scales or microsporophylls. There are two pollen sacs on each microsporophyll called pollen sacs or microsporangia. Meiosis takes place in the microsporangia and pollen grains are produced.

There are female cones, much larger than the male cones, usually found on the upper branches; each consists of spirally-arranged scales called megasporophyll. On maturity, these scales become woody. Two ovules are present side by side at the base of each scale. Haploid megaspores are produced in the ovule by meiosis.

Megaspore forms a female gametophyte which produced female gametes or eggs.

Fertilization results in embryo formation after which the ovule ripens to form seed. Female cones normally remain attached for three years on the plant. When matured, the cones open up and the seeds are set free and dispersed.

1 comment:

  1. The male cone produces pollen grains or microspores, it then enters into the necellar surface of the female cone i.e ovule, then the sperm and eggs fused to form an embryo sac, the ovule ripen to seed. The seeds set free and dispered and new plants are formed