The Evolution of Pine Tree Seeds

Reproduction proceeds by a process called pollination. This is when pollen is transferred from a pollen cone to a seed cone via wind. The seed cone secretes a liquid, to which the pollen grain sticks. This fluid is then soaked up by the seed cone until the pollen comes in contact with one of the two ovules at the base of the scale.  When many of the ovules have been germanized, the scales on the seed cone become thick and hardy and close up. Then, the development of megagametophytes ensues.  

The megasporocyte is initially diploid (2n). After germination, the mother megasporocyte goes through meiosis to create four haploid (1n) megaspores. Only one of these four, called the functional megaspore (1n) will go on to produce a mature megagametophyte. Upon maturation, a few (about 2-5) archegonium will be produced over the course of 1-2 years, each containing one egg.  

Simultaneous with the development of the archegonium, the pollen matures and develops pollen tubes. Pollen tubes provide the means of transportation of pollen to the egg, now fully developed inside the archegonium. The seed is now fully formed!

To learn more about seed evolution, check out The Seed Biology Place online by the University of London