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Friday, January 27, 2006

Reproduction of Gymnosperms

A group of plants called gymnosperms developed wind borne pollen. These were trees -- cycads, ginkos and needle-bearing trees such as pines and redwoods. Tall plants get more wind than those close to the ground, and the gymnosperms developed small male pollen-bearing cones. Their pollen was released into the air and drifted to other trees in the forest. Today, if you are in a pine forest in spring, you can often see a golden haze of pollen grains in the air.

The plants also developed female cones which are essentially ovaries. The pollen falls directly on the female cones, and the pollen grains grow tiny tubes into the ovary to find the chromosomes and join with them. The female cone grows into the cones that we are familiar with, and the seeds are tucked safely between the bracts.

Gymnosperm means naked seeds. These seeds have only a very thin covering that probably does not offer them much protection.

Wind pollination seems rather extravagant, as surely most of the pollen grains never find a female cone. However, the system works, and has worked for millions of years. Gymnosperms grow in forests and groves, where the tall individual plants grow close together, so there are many potential targets for the pollen grains.


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