Plants have developed many different ways to spread their seeds. Many plants have very simple reproductive systems. Simple plants like ferns, for instance, need moisture to move their seeds even a short distance. Many flowers simply drop their seeds as the flower dies. However, some plants disperse their seeds over much longer distances, so that they fall a long distance away from the parent plant.
Seed dispersal is a term that refers to how a plant distributes its seeds over long distances. While plants that simply drop their seeds as they die also disperse their seeds, dispersal is typically seen as a method by which plants spread their seeds over much longer distances. Trees have some of the most common dispersal systems studied by scientists, but smaller plants can have effective dispersal methods as well.
Wind is one of the best dispersal methods available. Plants spread seeds that are light enough to float freely on the wind for long distances before settling down. Some seeds are equipped with wings to help them flutter down to the ground. Other plants use water to carry their seeds, and many plants that live near water produce seeds that have waterproof coatings and can float. Other plants try to make their seeds attractive to birds and other animals so they will be eaten and then passed out with the waste in a different location. Other seeds are sticky so they will cling to the hair of passing animals.
One primary reason for seed dispersal is overgrowth. Plants, especially tall plants like trees, need as much sunlight as they can in order to survive. A seedling cannot easily grow up in the shadow of the parent tree, where sunlight is blocked out by leaves already there, and the water and nutrients in the ground are already taken by other, more established trees. Dispersal takes these seeds farther away to their own spot of sunlight and soil.
Sometimes it is not competition that is the problem for the seed, but just the right growing conditions. Older plants can survive in areas where seedlings may struggle to live. Dispersal allows seeds to move to locations where better growing conditions exist, at least temporarily. Several cones of trees, for instance, only open after fires, when undergrowth is cleared and the ground has been fertilized by the remains of other trees. Hand in hand with this is proper timing. The seeds may need to travel until warmer temperatures come and allow them to germinate.
Seeds, like other productive methods on the earth, help the species survive by spreading it throughout the world. The farther away the seed travels from the parent plant, the safer the species is. A tightly clumped section of trees can be easily destroyed by disease, plant-eaters, or natural disasters. But many different sections of plants over a wide distances can survive these problems more easily as a species.
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