Seed propagation is the main characteristic by which gymnosperms differ from plants that reproduce by spores.
Unlike flowering plants, gymnosperms do not form a fruit.
Consider the reproduction of gymnosperms using the example of pine. In spring, small cones of two types are visible on its young branches: male – greenish-yellow, gathered in close groups at the bases of young shoots, and female – reddish, sitting alone on their tops.
Each cone consists of an axis and scales sitting on it.
On each scales of female cones, two ovules develop, in which female gametes (eggs) are located.
On the scales of male cones, two pollen sacs develop. Pollen ripens in them. Ripe pollen spills out, and it is picked up by the wind, which can carry it over long distances.
If the pollen hits the female cones, pollination occurs. After that, the scales of the female cones are closed and glued together with resin.
Inside female cones, pollen grows into a pollen tube, in which male gametes – sperm cells – are formed.
The ability of gymnosperms to form a pollen tube, which carries out the delivery of immobile male gametes (sperm) to the ovum, is a progressive biological step in the evolution of plants due to life in a terrestrial-air environment.
In the ovules of the closed cones, fertilization occurs. From the zygote the embryo develops, from the whole ovule the seed.
In the seeds of gymnosperms there is a tissue containing a supply of nutrients – the endosperm, which surrounds the embryo.
Cones grow and woody (at first they are green, then they turn brown). When the seeds ripen (a year and a half after pollination), the cone scales move apart, and the seeds spill out of it. The seeds have a membranous “wing” that allows them to fly away from the mother plant with the help of the wind.
As a result of sexual reproduction in gymnosperms, seeds are formed, consisting of an embryo, endosperm and seed coat. The embryo of the future plant is formed inside the seed located on the surface of the scales of the female cone.
Vegetative propagation in gymnosperms is very rare.