Wednesday, March 18, 2015
The Wonder of Whiskers
Groundsel flowers self-pollinate and run to seed with remarkable speed. Each seed is carried aloft on a parachute (pappus) of hairs...but there are other, much smaller hairs with a different function attached to the seed coat itself....
The seed coat also has a covering of microscopic hairs, far smaller that the parachute hairs, that rapidly extend outwards at right angles from the seed coat when it becomes wet. x40
A forest of minute seed coat hairs, at higher magnifcation (x100) 
A single seed hair, magnified x400, using interference contrast microscopy that reveals hidden structures within the cell that the hair is formed from. Each hair is made up of a woven spiral column of threads, like a piece of string........or a water-absorbing wick?Groundsel Senecio vulgaris is one of the most successful colonisers of cultivated land, thanks to its capacity to grow rapidly, flower quickly and disperse its seeds far and wide on tiny hairy parachutes that will carry them over large distances. But it has another winning adaptation for rapid invasion of ecological niches too, that I only noticed by accident recently. The Latin generic name of groundsel – Senecio – means ‘old man’ and alludes to its parachute of whiskery, silvery hairs that transport the seeds on the breeze. But, as I discovered yesterday, groundsel has a hidden complement of hairs that are invisible to the naked eye that have a quite different function: anchorage and water uptake. I’d put some groundsel seeds in a drop of water on a microscope slide, to photograph their parachute hairs, and was amazed to see a mass of writhing, much tinier hairs begin to extend from the coat of the seed, until hundreds were extended at right angles to the seed coat surface. When the seed is dry these are pressed so close to the seed coat that you dont notice them, but once it’s wetted they extend. What’s their function? Well, my guess is that they anchor the seed to a damp soil surface and then act as wicks, conducting water to the seed and speeding up germination. Notice how, at high magnification, each hair resembles a woven piece of string. Groundsel seeds germinate and establish themselves as seedlings incredibly quickly, and my guess is that this surface seed coating of ‘wicks’ is a crucial adaptation for helping airborne seeds that have landed on the soil surface to take up water and germinate as quickly as possible.
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