麻豆淫院

Don't be disappointed if all the fluffy seeds of a dandelion don't fly away with a single blow. The gust of wind from your lungs may be strong, but the dandelion's natural desire to control how its seeds are dispersed is stronger. Researchers at Cornell University and Australian National University found that not all seeds are attached to the seed head in the same way, which creates a massive difference in the force required to detach them.

It takes much less force to break off the seeds in the positive direction (90掳 towards the capitulum or top of the seed head) than it does in the negative direction (90掳 towards the stem). Pulling a dandelion seed straight out is even tougher, as it would take over 30 times more force than tugging it out at an angle.

The findings are in the Journal of the Royal Society Interface.

Many flowering plants aim to disperse their seeds far and wide. By spreading seeds away from the parent plant, they reduce competition for limited resources and allow their offspring to colonize new areas, expanding their range. Some plants rely on animals for pollination, others depend on water, but the dandelion's preferred method is the wind.

Dandelions have evolved to develop pappus, the fluffy white hairs on the seeds, that provide special aerodynamic abilities, ensuring the seeds get caught in the air and float for longer distances.

Scientists believed that the dandelion was a passive character in the situation: the seeds went wherever the wind took them. This notion was soon challenged, as more researchers discovered that the phenomenon of non-random seed abscission, where the detachment of seeds from a parent plant is not purely arbitrary, but rather dependent on environmental conditions.

Scientists have known for a while that the seed dispersal mechanism in dandelions is dependent on the direction of the wind, but the underlying mechanism supporting this feature remained poorly understood.

To measure the force needed to detach dandelion seeds from different directions, researchers devised a clever setup. A microstage was set up with a dandelion seed head, including its stem, secured by a pin. A single seed was chosen, and the center of a seed's pappus was then glued to a surgical suture connected to a force sensor, mimicking the pull of wind.

They slowly moved the micro-stage to create a pulling effect and recorded the abscission force, which was measured as the peak force recorded when the seed detached. They explored how direction influences seed release by repeating the seed pulling action at various angles and directions.

They found that the force needed to detach a dandelion seed can vary by more than tenfold depending on the pull direction. The seeds detach effortlessly when pulled with the wind but cling stubbornly when pulled against it.

Pulling a seed straight out proved the hardest, requiring a median force of 45 mN, which is over 100-fold more than that required in the positive direction.

They also used microscopy to get a detailed view of whether the dandelion's attachment site is asymmetrical. The measurements showed that the side facing the stem has raised structures that brace the pappus and resist detachment, while the side toward the top is much weaker. This structural imbalance explains why the detachment force changes so much with direction.

The study establishes that while plants cannot control exactly where their seeds land, they can control how they detach.

Dandelions owe their widespread presence to this clever dispersal strategy, which ensures that each seed drifts to a new spot adorning the area with bright yellow flowers.

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