If you've got a green thumb, you've probably heard an old wives' tale that warns against planting squash and cucumbers next to one another in a garden. The story goes that if these two vines grow too close to one another, they will cross-pollinate and produce less-than-tasty "squacumber" hybrids. This story is, of course, absolutely ridiculous.
To understand why it's so ridiculous, you have to know a few things about pollen and its role in nature. For starters, you should know that pollen is to plants what sperm is to humans. Pollen spreads the male plant DNA that makes reproduction possible, so it’s essential that it reaches the female parts of a plant. Some plants, like flowers, can self-pollinate because the plant has both male and female reproductive organs. But not all plants have both male and female parts, and those plants rely on cross-pollination to spread genetic material. Insects, birds, wind and even water are all vehicles for pollen, and they make cross-pollination possible -- but only between plants of the same variety. So when we talk about cross-pollination, you can see we're basically talking about "the birds and the bees" as it applies to plant life.
Cross-pollination cannot occur between different species, and that's why the idea of an alien-looking "squacumber" hybrid sprouting up in your backyard is so ridiculous. That would be like saying your dog could get together with an elephant and birth a "dogephant." It can’t happen. The only way that two different plant species can combine DNA is through genetic engineering.
While it can't make hybrid magic happen, cross-pollination benefits the environment in a number of ways. The most obvious is that it allows for genetic diversity. With cross-pollination spreading good genes throughout a plant population, plants are more likely to survive. Another way cross-pollination benefits the environment is by promoting co-evolution. Co-evolution is a term that refers to a mutually beneficial relationship between two species. One example of co-evolution is the relationship between butterflies and the plants they pollinate. Since butterflies need pollen for food and plants need butterflies to spread pollen, each species has developed traits to aid in these goals. Plants that attract butterflies have developed very bright colors while butterflies have developed a strong sense of sight to see the colors [source: NBII]. Without cross-pollination, this symbiotic relationship couldn't be possible.
When seeds are extracted from plants that have been cross-pollinated, they typically produce stronger and more vigorous plants than those produced by self-pollinated plants. In fact, the production of varied, hybrid flowers and hybrid corn relies on the principles of cross-pollination.
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