Sunday, September 26, 2010

Cock's Foot Grass Fail-safe Mechanism
























The leaves of plants are wonderfully adaptable structures and, in addition to their normal photosynthetic role of trapping energy from sunlight and using carbon dioxide and water to produce sugars, they have evolved a wide variety of functions, ranging from the tendrils of peas to the showy petals of flowers, both of which are highly specialised derivatives of leaves. Sometimes these specialised structures revert to their original form, giving a  clue to their origin, and that's the case with this peculiar seed head of cock's foot grass Dactylis glomerata, which I found beside an arable field near Corbridge this afternoon. On the right you can see a normal seed head, dried by the sun and probably having already shed its seeds, leaving behind the papery bracts (known as glumes) that formed the grass floret when it was in flower and enclosed the stamens, stigma and ovary. The glumes are highly reduced, modified leaves but in the seed head on the left they have reverted to being normal leaves, becoming green and elongated, so each of the grass florets has become a miniature grass plant - a clone of the parent plant. This kind of behaviour, known as pseudovivipary, is quite frequent in late-flowering plants of cock's foot that bloom too late in the season to produce seeds and so use this fail-safe mechanism to produce a cluster of small clonal plants in the seed head instead. You can see florets in various stages in the reversion process - some are just going green, others are already fully-formed miniature grass plants. Eventually the stem bearing them will bend under the weight of the sprouting clones and it will fall over - and when That happens those miniature copies of the parent plant will touch the soil and root.

2 comments:

  1. A new word learnt- glumes. I have seen a similar thing happenning in the red ginger plant in my garden.

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