Tuesday, May 14, 2013

Elegant moss capsules

These elegant spore capsules belong to the common woodland moss called swan's neck thyme moss Mnium hornum and their presence is testament to the fact that the individual plants that bear them are female. Sometime back in the winter the egg cell inside a microscopically small flask-shaped structure called an archegonium, tucked away somewhere down amongst the leaves,  was fertilised by a swimming male cell called an antherozoid, that swam across the surface film of water on the moss plants, attracted by organic acids secreted from the neck of the archegonium. Countless similar sexual encounters between moss plants occur every day on the woodland floor on mild, wet days in winter and early spring.

And these are the structures that release the male sex cells. The glistening structures packed amongst the rosette of leaves on the shoot tips of these male plants are the antheridia - flasks full of male antherozoids, each equipped with a whip-like flagellum that propels it through the film of water. Sometimes rain-splash in the rosette of leaves will hurl water droplets laden with antherozoids towards surrounding female plants. Sometimes small soil animals may carry antherozoids on their bodies.  The odds against a successful fertilisation are long but the antherozoids are many and the net result is a fertilised egg cell, and ultimately a spore capsule full of spores that will be dispersed on the wind and grow into a new moss plant. Mosses have been reproducing like this for over half a billion years, surviving five great mass extinction events that have extinguished many other forms of life. 

Durable little plants, aren't they?

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