Why is water needed...?

Question

Why is water necessary in the reproduction of ferns?

Answer 1

The ferns' sex life is pretty interesting. Let's begin with the spore. The spore germinates in an environment appropriate for its development. Cells divide like crazy, but the plant body that develops from the spore is not the fern we may be expecting! Rather, the object that results when a fern spore germinates is a tiny prothallus, illustrated below.



The ruler marks at the bottom of the picture on the right are 1/16th of an inch apart -- about 3 mm -- so the objects you see there (which I just collected from a deeply shaded cliff near my home) are tiny. Before explaining what you see there, let's consider the diagram at the left.

The heart-shaped item in the diagram is the fern prothallus -- the thing that forms when a fern spore germinates and the cells divide for a while. A mature fern prothallus has the following:

rhizoids --primitive filaments that serve the prothallus as "roots"
antheridia -- the fern's male sex organs, which produce sperm
archegonia -- the fern's female sex organs, which produce eggs
When fern prothalli are mature and water is present, sperm swim from the antheridia through the water to the archegonia, and when a sperm fertilizes an egg in an archegonium, then a zygote is formed, and this zygote develops into an embryo, which eventually grows into a fern of the type we are familiar with. Ideally, the sperm from one prothallus fertilizes the egg of another prothallus, thus mingling genetic material form two different plants.

Answer 2

water is the medium of transport for the ferns sperm. Without it, it could not fertilize its eggs.

Answer 3

Water is the key to all life ( as we know it )